I have run into a weird situation that ends up with duplicate control IDs on
a card which I thought couldn't happen.
The scenario is that I copy a group containing two field controls from one
stack to a group in another stack. After copying, the two field controls
both have an ID of zero! Needless to say, this plays havoc with anything I
do that tries to access the fields.
I have worked around the problem by creating a new group, then copying the
two fields individually from the source group to the new one and that works