Field content in background group only visible on its 'parent' card?

[Keith Clarke]

Hi folks,
I have a background group containing a sub-group, which in turn, contains a button, plus an overlaying field that contains the button's Title (as I can't align the button's name against its 'icon' images appropriately).

This Title field is selectable on all cards in the stack but the content text is invisible on all cards except the one where it was created.

I've tried removing and replacing the background group but no change - and new cards have the same problem. 
Any clues?
Best,
Keith..