A bug or else: cant update user prefs via forum?

Hello.

Before I even think to fill up a bug report, Does anyone have the same issue like I do: Some Details EE2.10.1 with Forum 3.1.19 running with PHP 5.6.2 Forum Theme: eeBootstrap. (All I can think is that this theme is the reason for errors).

When I go to Forum, I cant update my preferences.

So, If I try to de-select option from like: Accept Private Messages sent to you by other members of this site

I get this error:

THE FOLLOWING ERRORS WERE ENCOUNTERED The action you have requested is invalid.

NOTE: When I go via CP (backend) I CAN update my preferences.

So, is this a bug on my installation, or can someone duplicate this on their end? Ideas how I can track down the reason? (holding my hand-help cos Im poor with debuggin).

Thanks in advance.

PS. I sure can edit my avatars, photo, locations etc. etc. via forum with no problem. So far only preferences are the ones that I CAN’T update and getting the error above.