It's a very late reply, but anyway:
It depends on how the people see these troops. If they see them like oppressors, they will be oppressors. In Crimea, different thing happened. They just didn't see them in that way. I think.
That is not the point. Even if we assume that a) Crimea wants to join Russia and b) Crimea wants Russian soldiers as protection, that doesn't mean the Russian intervention was right. Putin could have used diplomatic pressure to achieve these things. He could have trippled the gas prices. He could have let elections happen in Ukraine and support a constitutional change that allows for Crimean independence. He could have involved international organisations. There were a lot of options and he chose the one that he knows everyone will understand as a massive disruption of international stability.
The reason why the Russian leadership decided to use force is probably based on past experience of trying to defend its interests from Western actions by diplomatic means. For example, Russia and China were against NATO's "humanitarian bombings" of Serbia in 1999. NATO simply started bombing Serbia without the UN's consent, and Russian resolution condemning it didn't do anything because America and its allies voted against it. Russia's current Foreign Minister Sergei Lavrov used to be the Russian ambassador to the UN back then, so he certainly saw it first-hand.
As a result, people in charge of Russia, looking back at all that, probably think that diligently following 'international law' while Russian opponents constantly violate it under various noble pretexts is incredibly foolish and harmful to Russia. They assume that it would be naive to expect the West to follow international law if the West has no qualms about violating it. Thus, the only way to defend Russia from Western actions violating international law is committing actions violating international law.