Brush presets of Bristle and Filter engines are marked as modified by selecting them and just switching to another preset without any modification. This is a bug relayed from the local community. Tested 4.4.5 and 5.0 nightlies, Windows and Linux. I was only able to confirm the Filter brush engine presets are indeed affected: x)_filter_blur x)_filter_sharpen I don't know which preset uses the Bristle engine, so I was unable to confirm that.
I can confirm this. Filter brushes seem to have been affected by this for a while. For Bristle brushes (Ink 8 Sumi-e) this seems to have started in 4.2.7. Both engines are still affected in the Krita 5 beta. Should this be marked as a regression?
The Filter brushes appear to have been fixed in 5.1.0. The Bristle brushes are fixed in 5.2.0-prealpha (by https://invent.kde.org/graphics/krita/-/merge_requests/1334).