I'm assuming that only happens when you modify a creature that was loaded from a save? If so then this bug must have existed ever since I introduced saving and loading (I think I know why it happens). I'll put it on my todo list for whenever I'll have time to work on the next update.
When you say "more static" do you mean that they move less in general or that the bones feel more rigid? Also, do you only experience this when loading old evolution saves or also with new simulations?