Yeah this is why it's so confusing. With the track cut (and it's really cut .. ) GLUE, MMU and Shifter DE still have continuity between them. However, the trace I cut obviously does something else (it goes upward and I lose it underneath the WD1772) since the computer stops booting. Repairing the trace fixes it again.
And it really is DE, I'm not cutting something else ..
Oh well. That's an investigation for another day ... I'm really eager to get the "Stefan-mode" working now and then see if resyncing the clocks can fix the floppy ...