So Eagle has suddenly decided that the DRC rules don't apply - I'm getting hundreds of errors about the widths of traces being too small (at 3.5mil) even though the settings are set to allow that...
I also noticed that if I start to route a wire, it wants to do it at 6mil, and if I go to change it to 3.5 mil from the pulldown, it refuses the change and puts it back to 6mil...
It was perfectly ok with all of this yesterday - but apparently something changed. Is there some option I might be missing that says "override the DRU" ?
Kicad looking more and more appealing, but this is a relatively complex design (I'm up to 11 pages of schematic now) and I didn't want to jump into a new CAD package with that sort of project...
[edit, about 5 minutes after posting the above (of course)]
Leaving this as a warning to posterity - never assume there isn't a PEBCAK...
Yesterday I was working on the BGA side of this, today I imported parts of another design, and apparently merged my net-class lists during the import - I do recall a warning dialogue or two, but it didn't twig at the time... The minimum size of the default net-class on the other project was 6mil, and so everything on the board that was narrower than that was immediately flagged.
Changing the net-class rule for the default net was all that was required...