Hi, @Reinold and @Vitamorus!
Thank you a lot for the help with triaging bugs! I just followed your changes on bugzilla and fixed recently-confirmed bugs! This way together we have managed to fix at least 12 bugs this week 
I have also fixed two other bugs, but I need some testing from people before I merge the changes:
- [need feedback] Fixed sorting of last-used colors in the popup palette
- [need testing] New opacity handling in the brushes needs testing by users
I have started separate threads for them. The second patch is for the bug confirmed by @Reinold (356462 Conversion from integer to float and back gives rounding errors for opacity)