All, This report is just for documentation; there is probably no action needed on the part of the maintainers.
I have 3.22.1-3+deb9u1 installed on my system, and the evince.thumbnailer file has the same double-semicolon problem in the same location as the evince.desktop file originally reported. I downloaded the source package for evince-3.26.0-2 and verified that both evince.thumbnailer and evince.desktop have been fixed - the double semicolon is gone from both - so that is OK. However, I also wanted to note that the double semicolon was probably also causing an incorrect entry in /etc/mailcap to be created when evince was installed, which was causing another application (alpine) to have trouble reading /etc/mailcap. An excerpt of my /etc/mailcap follows: --- application/vnd.comicbook+zip; evince %s; test=test -n "$DISPLAY" application/x-ext-cb7; evince %s; test=test -n "$DISPLAY" ; evince %s; test=test -n "$DISPLAY" application/oxps; evince %s; test=test -n "$DISPLAY" application/vnd.ms-xpsdocument; evince %s; test=test -n "$DISPLAY" --- alpine was looking for a mailcap entry that was further down in the mailcap file, but it stopped searching when it hit the line starting with "; evince". It's probably alpine's baby to handle poorly- formatted mailcap lines better, but it's also good to not put poorly- formatted lines in mailcap. Again, I am pretty sure the mailcap entries were generated from one of the two files that were fixed, so future installs of evince should write correctly-formatted lines to /etc/mailcap. Thanks! Matt Roberds