Just a little bug in the latest Arena version (disovered it quite some time ago, was probably in earlier versions as well .. sorry for the late report):
Set a Layer to Auto Transitions of i.e. 1 sec length, have a clip running that is set to Play Once. Than click on a second clip on that layer. The transition is done as expected, but as it finishes both clips get stopped, the Layer is cleared.
Hope you can fix it,
thanks and bests,