Comment # 17 on bug 1102110 from Martin Pluskal

(In reply to Stephan van den Akker from comment #13)
> The error messages about grass and qgis-plugin-grass are gone now when
> uninstalling libproj12. So, on my system nothing prevents me from
> uninstalling libproj12 any more.
> 
> The remaining concern is that libproj12 remains on systems and causes
> problems in qgis an perhaps grass (see comment 11). IMHO these programs
> should explicitly call libproj13 or force the removal of libproj12.
So if I understand correctly, issue was solved by rebuilding affected packages.

Forcing removal of old libproj would be challenging - as in violating packaging
rules/guidelines. We have differently named packages with libraries in order to
allow installation of multiple versions at same time.