I think it has to do with the 81 script being 'broken'. This then 'breaks' any script that is inherited (?) by the broken script.
As for the signals. This is a fairly wide spread problem. It's to do with the signal attempting to do things that signals shouldn't be able to do (setting a speed limit IIRC) in Trainz. There were attempts to find a 'mid ground' if I remember right, but the problem was that they would conflict with too many scripts in Trainz, and be too easy to cause crashes. You'll find that many of the European signals have the same problem.
Zec
Edit: David, you really need to find some better smoke textures for that 38They look too much like the standard Trainz ones. I would suggest using LieLestoSbrat's smoke set. Look really nice IMO
Also, if you name the cylinder drain smoke effect attachments (if you have any) 'a.drain0' 'a.drain1' etc, they should be able to be turned on/off in TC3/09 (plus you can set the max speed for them for 04-TC2, so they aren't on all the time).
Yeah, that's why they're not ready yet.
I'm afraid I'm not "steam literate"

I was about to attempt a twinkles set for the 38 but I'll have a look at your suggestion first

Thanks
David