I see this issue started somewhere between MESS 0.133 and 0.134. The C64 related entries in the whatsnew.txt for 0.134 were:

- [C64/C128] Implemented new VIC II core [Christian Bauer, Roberto Zandona']
- [C64/C128] Fixed TAD in CIA6526 [Roberto Zandona']
- [C64] Implemented some cart type [Fabio Priuli, Roberto Zandona']

I'm not sure how I could narrow it down to a particular SVN update. Does Bobz keep an archive of his daily builds somewhere?