So, we fired up FSX this morning so I could show Hugo all the good stuff I did to the panels last night and...disaster!
When we opened the saved flight for the Baron 58 the main window was no longer stretched across all 3 monitors, but was the same size as the actual FSX application window the main interface that opens when you start FSX and plays that godawful music which I actually kind of like now). Also, although the main panel was still undocked and on the instrument monitor, it was squashed into the left 10th of the screen. The cursor was doing that spinny thing as well, which is never a good sign :(
Despite numerous restarts I couldn't shake the problem, which affected all aircraft, and to add to my annoyance FSX stopped shutting down properly. The window would close but it was still running in Task Manager.
To cut a long story short I figured it must be something to do with the panel.cfg edits I'd been making last night, probably one of the last couple as it had been working like a charm earlier on. I restored all the original cfg files and hey presto, FSX started playing nicely again. I had my suspicions that it was the Beaver causing all the trouble and, sure enough, when I started using my modified file for this plane FSX freaked out again.
I've restored the C172, Baron 58 and Goose for now, and I'll work through the rest later. I'll do one at a time and test carefully to catch any problems right away.
While looking at the Beaver's panel.cfg I remembered seeing a warning when I loaded it into FSPanelStudio. I tried again and got a message telling me that two panels had the same name: FLAPS_PANEL.
Wondering if this was the cause of the problem I edited the file, changing the first FLAPS_PANEL to FLAPS_TRIM_PANEL (I got this from here), and the second to TRIM_PANEL, but it made no discernable difference. I can't even load the plane for Free Flight without the cursor going mad.
More research is clearly required, as I love flying the Beaver (that sounds like a euphemism), but it's not a priority right now.