I dont think they're too bugged and I cant claim to know the system inside out, but I can offer some advice on how I get mine to train:
I know marksdwarves are pretty bugged, but I want to make sure I'm not overlooking anything. Here are my problems:
1) Archery Targets: Marksdwarf squad has a barracks with bed, cabinet, etc assigned for sleeping, indiv and squad equip (NOT train). Archery target is assigned for training. Dwarves never train at archery range. Why? (Set to train during all months of schedule, training alert is active).
I have a large barracks, in which all the archery targets are set up. ie: All the targets are activated, and assined 'TQI' for each squad. The barracks is also set up with 'TQI', and covers the archery targets and their ranges. My dwarves were not training recently as despite several RL years playing, I had the ranges N-S, and the assignment E-W on the recent ranges.
So that can be worth checking. I dont see any problem with having Training set for the barracks, they sometimes do Dodging practice, which can be helpful in survining goblin return fire.
2) Equipment: Marksdwarf squad set to use "Individual choice: ranged." Fortress has plenty of crossbows, ammo, and quivers. Squad is set to 1000 bolts for combat, 200 for training. Only 1 or 2 dwarves actually have bows that they use (I used some goblins for target practice - 1 dwarf shot while the others stood there). What am I overlooking?
As previous posters, I stick to assinging them Crossbows. I think there is a problem / bug if one squad has both bows and crossbows, then they are going to need arrows and bolts, and might end up with quivers full of the wrong ammo? I stick to crossbows, as it works for me.
Also ensure they have quivers. Worthwhile adding flasks/waterskins/backpacks to enable them to last longer before returning for food and drink.
3) Schedule: Squad is set to have 2 people stationed in a tower, and 10 to train. This alert restricts the 2 guard dwarves on duty to a burrow right behind fortification walls (no "station" order, just "restrict to burrow"). Alert is active, make sure that the correct burrow is highlighted and squad is set to it. Nobody guards the tower. Does the order that orders are in count (in this alert, first I order "Defend burrows - guard tower [2 minimum]" and then "train [10 minimum]." Is the "train" order drawing from the people who should be on duty in the tower?
I think this is where the problem might lie. I think there are two isses. The first, I dont understand how the guard burrow and training can be happening at the same time. My understanding is that a squad is either doing one thing or another for each month. Perhaps this can be done, but I wont be able to help here.
I can help with getting them to train. Once they're trained, you can move them manually, or investigate other options for patrols and guarding. I have mine train 3 months on, 3 months off. This seems to avoid bad thoughts from long patrol duty. They also train in their free time, so that also helps. I also assign all my marksdwarves as hunters, so if they do want to work, they are also live training shooting as well. Then just need to ensur that each squad has a barracks which includes archery ranges assigned, and those archery ranges assigned, and they are set to Active/Training, with a 3month on/off schedule. Next - the months they are on need to be edited: It defaults to Train - 10 Minimum. What this means in practice is that they wont start training until there are at least 10 dwarves ready to start. In practice a squad of 10 has several drinking, eating, sleeping or upgrading equipment at any one time. This is important to note, because it means they wont start training until all 10 are ready in the barracks, which in reality means never. If I have a squad of 2, I am happy to have minimum 2, but I would keep minimum 2 for squads up to 4, then stay at roughly 50%. This is a minimum, if there are more there, more will train, but if there are less, then they will all hang around waiting for the others to finish eating and drinking, and by the time they do arrive, the first lot has got hungry and thirsty and left!*
Other random military question: I hear to train melee dwarves without any weapon skills, it's best to let them conduct individual drills in their weapon. I'm told the way to do this is set a train "2 minimum" order and make it active, so 2 guys will do demonstrations/spar while the other dwarves do their own drills. When I activate this order, 2 guys do their military thing and the rest of the squad becomes civilians. Why?
In general I train melee dwarves the same way - a single barrack set to 'TQI', and 3months off/on with a 2 minimum, and the Alerts set to Active/Training. A completely skilless set of dwarves will start with demonstrations, and will gain skill very slowly. Once they reach a certain level they start sparring and gain faster. They will train when the schedule tells them to, with the icons turned to 'soldeir' (solid in the ascii), and also undertake individual training when off duty. You can assist this by turning all their other labours off, but it is dependant on each dwarves personality. I then try and ignore them for a while, and generally when I look back later, they have gained a bit in skill. Dwarf Therapist is very useful for checking skill gains as it shows the XP level in addition to the general skill level description. So you can skill the skill points rising for each training bolt shot for example. More than anything else, this is just reassuring that it is all working!
Dwarves also learn fastest from someone with more experience. This is why hunters are useful in Marksdwarves squads, as one dwarf with skill soon passes it on. For this reason I generally build squads around whatever skills the imigrants bring, even if it is in a less than ideal weapon. This last game I have taken to having many squads, each of only 2 dwarves. Quite impractical to manage, but interesting to see the different squads skill up at different rates.
Hope that wall of text helps a bit!
*I dont know what the downside for leaving it at minimum 2 for all size of squads? Now I type this, I dont see why I shouldnt stick to minimum 2 for all squads.