An ongoing mecanim crossfade cannot be interrupted by another crossfade or even a straight up play call, meaning that sometimes an animation could be ignored or delayed if the call happens during a crossfade transition, which in turn makes gameplay clunky and unresponsive at what seems like random times. This needs to be fixed.
Look at how Legacy handle crossfade interruption: this is what it should be doing.
I also posted a feedback for this issue here: http://feedback.unity3d.com/suggestions/allow-mecanim-crossfade-function-to-interrupt-an-ongoing-crossfade