Weirdly, after I removed the gih files I did notice many presets "red-crossed", but those presets were for some using autobrush!

As if every preset using autobrush also remembers the selected predefined brush, although it doesn't use it at all (as it uses autobrush mask instead...).

So I selected each autobrush-based preset marked invalid, as they still 
loaded fine, selected another predefined brush and back to autobrush and 
re-saved them. No more red-cross then.

Reproducible: Always

Steps to Reproduce:
1.select a predefined brush, then select autobrush, save preset, close Krita.
2.Delete the predefined brush file you selected at first step.
3.Open Krita, the autobrush preset just saved is now red-crossed.