Gathering profession mastery is negative

Bug Name:

Gathering profession mastery is negative​

Bug Description:

It looks like I have a permanent -400 applied to my gathering mastery.
Without any gear on I should get 360 gathering mastery from my gathering skill level, but I actually have -40, which is impossible. Even with gear I get the permanent -400, I should have 360+220+400+40 = 1020 mastery but I get 620. My other characters don't seem to be affected by this bug.​

How to reproduce/proof:

It happened while I was gathering, probably when I leveled up my gathering skill. Reequipping items doesn't fix it and neither does relogging.

Here's a picture without any gear on: https://i.imgur.com/s6KCFQc.jpg
And another picture with all my gear on: https://i.imgur.com/EZ3Jqhr.jpg​

 

Quick update (sorry for double post): Another guildmate seems to have a permanent -50 on her mastery level. I now believe it has something to do with unequipping and reequipping the gathering clothes since I get 400 from my PEN manos gathering clothes and she gets 50 from her +11 Carthage Kits.
When she and I have our clothes equipped we still get the normal +400 and +50 though, despite the -400 and -50.

 

This is happening to me as well with a +6 gathering costume