Brush tip problem discovery
Regarding the “Importing brushes (brush tips) in the Brush Editor sometimes do not work anymore” problem. I continued working on the brush pack, and I found out partially what is happening.
It seems that most of the brushes I import are deleted by default. Sounds weird, but they are imported as a deleted resource.
In “Settings → Manage Resources” I checked “Show deleted resources”, and there the brush tips I tried to import appeared. Weirdly enough the default for me is that they are most often “deleted”, so when I select the brush that wouldn’t show up, and press “Undelete Resources”, then they appear in the Brush Editor just as I wanted them to! Weird
A suggestion for the Manage Resources window
The new Manage Resources window is brilliant btw! It’s a lot more informative and helps me a lot in brush creation. One thing I would have loved as well, was if you select a resource, say a Brush Tip, then a list of what presets are using that resource is displayed. That would be very useful. That way I could clean my resource folders without having to fear deleting a resource that a preset of mine is using. Or knowing if I have assigned a brush tip that is not supposed to be assigned something. Checking this manually is a time-sink when working with a lot of unfinished brushes. (I should probably write a Feature Request for this)
Overwriting Brush Preset warning
I also want to bump this feature request. It’s not a bug, but it almost feels like one, as especially beginners might panic if they click the wrong button when trying to save a new brush preset. People are not used to programs that are smart enough to do backups like Krita 
Though, recovering the preset is a time sink each time I press the wrong button on accident. If it’s worth the time, I think it would be a great feature in Krita 5 to make the brush management feel even more complete: