Charactercolors messed up after Standby

[joschhh]

Hello Mate Friends,
I observe following behaviour about 1-2 per week : When I reactivate after standby the color of most characters is set to the background color. So for example suddenly, on the login mask, I only see he "k", the ":" and "a". All other characters are blended into the background. The dialog still works fine and switching to another user is possible. The global login and the other user UIs are unchanged and normal. Yet logging back into the account in question, I need to navigate by heart to close documents etc or simply shut down the computer and reboot. Standby/resume or Hibernate/resume does not solve the problem.

Environment :
* Hp Elitebook with first Linux Mint 17.2 and 18.1, now with 18.2 and standard theme.

Note : It might be a theme related problem, because the issue only shows up with the standard themes sofar, I have not spent enough time on "user" themes however to be sure.

Any ideas ?

Josch