I quickly checked the Mossie out in CFS2 as I don't have CFS1 installed right now. There's definitely a bug somewhere, possibly with the way it's configured as it includes a separate AI Only drone. It works fine in CFS2 if you tweak Aircraft.cfg to use the AIR file of the flyable version but this is not the ideal way over it. The AI drone might cause a problem in FS98.
This might take me while to figure out as it's been a while since I used this method of configuring aircraft & my memory ain't what it used to be.

PS. From your original question the aircraft is listed on the selection menu. If this is the case the MDL Repair Utility should fix the problem. It's a conflict with WinXP. You would need to patch the MDL file of both versions. (In the model & model.ai folders)
I can't try this myself as I'm on WinMe.