Thank you for your efforts! Sadly this is still an issue in 15w45a. 😞
I just tested this (again) in 15w44b using the same setup you see in the screenshots. Can confirm for cows, sheep, spiders/cave spiders and witches (I did not test all the mobs again).
Things are a little different in 15w50a: The bug still seems to be the same for pigmen, creepers and animals. Zombies and skeletons show inconsistent behaviour: sometimes they walk back, sometimes they don't. I was unable to test this for witches; for some reason they don't want to walk over the trap doors any more (I assume this is a different bug that was introduced recently).