Just in case anyone else is having this problem, here’s more information I found out: I tried a 95 mbps 16gb SanDisk Extreme Pro to see if a faster card (faster than my 60 mbps 128 gb card) would help with the spanning problem on my GH3. It didn’t.
So I’m still having problems when I import MOV 50 mbps IPB files from my GH3. The MOV files do not import as a single, seamless file, the way my AVCHD videos do. And when the MOV files do import I don’t get audio with the MOVs. After reading online about this I came across someone who suggested dragging/dropping the MOV files onto my FCPX timeline, rather than importing them in the usual way. This turns out to be a usable workaround, because once the MOV file lands on the timeline FCPX automatically loads the MOV file in the event browser, too. And the audio is retained.
I still get an audio jump between my MOV files when I play them back on the timeline, but I found that if I create a compound file in the event browser, the new compound file will play back without an audio jump.
Seems like an odd way for things to work, so my guess is I’m still doing something wrong with my MOV video settings in the GH3, but at least this seems to work.
Anyone else have experience with this?