"Your timezone is not available. Please choose another" - after upgrade


Hi,

I did a test upgrade from 7.1Sp2 through 7.2 to 7.3.c.1 on my Windows 10 laptop. All seem to work fine (till now!) except that I get an error when trying to change User Preference settings in Admin. The error is "Your timezone is not available. Please choose another". Nomatter which timezone I choose (except when I set it to none) the error comes up on saving even without any modification.

Table Custom_captions (timezoneDelta and timezoneUTC caption families) contains all relevant GMT and UTC captions, including mine that is GMT +2:00.

Editing the Sytem Behavior, server timezone field saves fine, and this is set to GMT+2:00.

Another fresh install of 7.3.c.1 shows the timezone setting as UTC+2:00 which is what Windows 7 and 10 use.

My first thought would be to switch to UTC. How?

Any other suggestions?