Gwent Forums are down and I'm going to forget this shortly, so... someone please pass this bug along.

First I played Geralt, the gold card which has over 10 strength.
Then the oppnent played a card that made a gold card turn to silver targetting my Geralt. (wtf)
Then I used promotion to turn him back to gold.

Now the bug: After all that, I could NOT use a mutagen on him AT ALL.
Not as a normal unit, not as a witcher.
It would however allow me to use it on an enemy unit. :-(

If you do pass this along, thanks!