The problem is related to
System Settings > Application Appearance > GTK+ Appearance
changing GTK + styles, Widget style (dropdown) to Raleigh made Inkscape and GIMP work properly. After launching both apps, changing that Raleigh to oxygen-gtk made them look purdy.
This "bug" should be closed or moved to a forum.
The problem is related to
System Settings > Application Appearance > GTK+ Appearance
changing GTK + styles, Widget style (dropdown) to Raleigh made Inkscape and GIMP work properly. After launching both apps, changing that Raleigh to oxygen-gtk made them look purdy.