MUI trouble (The Bar, Nlist, TextEditor)

[itix]

Yesterday I discovered a possible cause, i.e. a reproducible bug: I start the MUI prefs program and whenever I access (by clicking on the list) to the preferences of "The Bar" or "TextEditor" or "NListtree" I get a guru $800000B.
Using a backup, I restored the versions of these classes I had on July, and they have no problem.

It means one of those classes is buggy.

What could be wrong on the A1200 ??

Nothing. While classes maybe work on other systems it does not mean they are bug free. Since your Amiga 1200 has 030 but your Amiga 4000 has 040 and 060 it could be possible those classes are using 040/060 only instructions.

[itix]

I was also thinking of some problem with 030 but... is it possible that nobody has noticed it yet? Yam 2.5 is out from almost 2 month, and betas were there since years...

is 030/50 not used anymore??

I dont think any of developers are using 030 anymore. Everyone is either on PPC or UAE. And it is not necessarily related to YAM but to one of those 3rd party MUI classes which triggers bug only in certain setups.