A tab control has different settings (in inspector) for active / inactive / hover / focus. Select the inactive and format it differently ?
(Btw: there are no attached examples to your post)
Apologies, I realised - here's the attachments.
I'd checked the 'Active/ inactive etc' settings - no difference.
I suspect it's something to do with the theme and a had a similar problem with tab inflexibility some time back (pointed out by Beverley) but I can't remember the exact syntax to look it up yet.