Another (maybe) related issue: in the tag panel, a tag has a grey background. The tag is not selected. If there is not a tagged item, a dark grey rectangle hides the tag.
If I select other tag, it has a blue background, while the previous remain grey.
If I select other tag, it has a blue background, while the previous remain grey.
Thanks for your attention.
Here are the screenshots (link updated):
https://imgur.com/a/6R7ko
Linux Mint 18.1 Serena;
Mutter (Muffin)
Mint-X
It happens randomly, not always.