I have upgraded to FCPX 10.3 and the only problem I have so far is with the range tool.
I work with several projects/timelines open at one time often copying a range of clips from one project /timeline to another. In the past it was a pretty simple process to select a range with the range tool on one timeline, copy and paste it into another timeline. Now that process doesn't work. Am I missing something? I can copy the selection (Comand+C) but can't paste it (Command+V) anywhere, even the paste option in the edit menu is greyed out.
I use this so much that it is really frustrating not to have this short cut. At the moment I am cutting clips, copying and pasting into other timelines. It's a work around but it was soooo much easier using the range tool, fewer steps.
Try trashing your preferences. Quit FCPX. Then, while you launch FCPX, hold command and option. You will get a dialog box asking if you want to trash preferences, say yes. After FCPX launches, check to see if the range tool works as you expect it. If it does, open the FPCX preferences and reset them how you need them.
I quit FCPX, dumped the FCPX prefs and restarted the computer. The range selector did not work in my current project even though it was created from scratch in FCPX 10.3.
After experimenting a bit I came to the conclusion that moving forward it should work as long as I am creating a new library with a new event and a new project. The range tool will not work in anything I created prior to reseting the FCPX10.3 preferences, even though those projects were created with FCPX10.3
I would conclude that this is a bug that manifested itself after I upgraded to FCPX10.3. Next time I will reset my prefs after I upgrade. I must have spaced on this one.