I noticed when using the 8-Direction Behavior that VectorX becomes a non-zero value when the player is moving ONLY Up or Down AND VectorY reaches its maximum speed. It also happens when moving only left but NOT when the player is moving to the right. In that case the VectorY always remains at 0.
I made an example C3P file: https://www.dropbox.com/s/kps3wxhy0r9nl0r/8dirmove_TEST.c3p?dl=0
I'm using r234.2
It looks like a bug, but maybe I'm missing something.