Jonny, just read your July 5 problem as I searched for a solution to my similar problem: I also upgraded to 10.3.9 last week then the problems started: specifically, clips play fine in the timeline an on the external monitor going FORWARD, but are jerky backwards (looks like circa 1910 newsreel at 18fps). If I turn off the external video it plays fine at real speed going backwards in the canvas window.
the media is on internal harddrives (not startup drive where FCP program & FCP project files are)
My boss has deemed this “unacceptable”
The tips re the canvas window not touching the edge helped with some crashout issues, but not the jerky motion.
I trashed prfs, restarted, reset prefs. No joy.
What did you end up doing?
Anyone else have tips?
Other prob: one clip refuses to accept a dissolve: it just freezes up at that point, pauses, then catches up. This happened while on OS 10.3.8
Juli
fcp 4.5, single processor G4, 1.47 gHz speed CPU; 1.12Gig memory; internal hd dr are: 38 gig startup, 114 gig ATA; 115 gig ATA on scsi bus; plus 2 ext firewires; 133MHz bus sp; 0S 10.3.9