I've searched and couldn't find others who may have came across this oddity.
I render slate graphic info for closing graphics for some videos. i.e. dates and times of upcoming events.
Sometimes those dates change. I typically export from photoshop or AE a still.
When returning to FCP X the rendered transitions, typically a fade, retain the previous graphic.
I do realize that rendered transitions can stay in the cue and as I do not change file names the system keeps
the relationship with what has been there. I have deleted transitions and added new ones and the previous graphics
still retains their inclusion. My only work around is to slip the graphics clip so it doesn't recognize the graphics "time presence". I agree FCP X is trying for speed here, but I wish it could understand update times regardless of file creation and include updates in rendered transitions etc...
Fill me in if you can give me what is UP!! Disclosure - I do not use Motion ( please don't say I should ).
I have recently had a similar problem with minor changes to titles not being rendered when outputting and overwriting an existing file. FCPX doesn’t output a new file, presumably because there’s no flag to say that what I’m trying to write is different from the file that’s already there.
Deleting the file from the disc first or saving (sorry, sharing) with a different file name works. I suggest you delete render files and the target file on the disc. It looks like there is at least one bug to report here.