I download regularly from Danbooru with apostrophes and other symbols (series queen's_blade, artists like homare_(fool's_art) or lin+). No problems, symbols appear correctly. Maybe it has to do with the option 'Replace underscore with space in Tag'.
I tested it with Gelbooru, there it works. The problem seems to lay on sankaku complex.
I also noticed some strange behavior with my tags. Look https://puu.sh/tdA0G/cf3f306480.png
As you can see, I downloaded 10 pics of queen's_blade with the copyright tag on first place.
But none of them are showing the queen's blade copyright tag, only the queen's blade vanquished queens copyright tag. Instead of queen's blade, they are showing "_" .
Yes I already unchecked "Use Global Tags.xml"
Admin if you are still alive, please help!