Site Actions Menu randomly disappearing

Hi,

We currently have a situation were the Site Actions menu/button randomly disappears for users that should have site owner permissions. The Site Actions menu will appear for a short while after assigning site owner permissions however will disappear shortly after. The only way I'm able to get it to display again is to remove owner premissions from the user then re-add them again.

Has anybody seen this behaviour?

Further information:

Using SharePoint 2010;

Using Claims Authenication, Trusted Identity Provider ADFS;

Thanks,

Ben