they will always move if, in the prefs menu you have full overlap selected, regardless of wether you had enough media or not, which is a bit stupid IMHO.
If you have Available media selected, FCPx will try to apply the transition with what’s available and will shorten its duration if available media is shorter than default transition. In this case, unless you are at the very firts frame of the media, it will not move it.
Whilst trying this out, I found out that because the default transition is centered and you can’t change that (another stupidity), FCPx needs a minimum of 3 frames to complete a transition.
I have not found a way to make a 2 or 1 frame transition, wether by defaulting it (another stupidity: transitions are expressed in seconds…) or by trimming it.
At least not in PAL 25…
There is a long list of things for Apple to fix…
hope this helps
Patrice Freymond
Senior editor
FCP Certified Trainer
patrice@monteur.tv