That it certainly pays to show a little more attention when copying things into PM questions - and more importantly, in looking at the differences between the modules in question in my case.
The basic issue shown is that the eval'led reload module overrides the local suppression of warnings, as it should. I thank the monks for explaining this to me, I was kinda there, but not quite.

However - the reason foo did not warn in my local examples - tested before posting - was simply because I didn't have 'use warnings;' in that code - and didn't spot that it wasn't there, ridiculously enough. And, in my haste, I manually typed the examples into my SOPW question - and magically added the 'use warnings;' which was the entire crux of the issue. Like, duh.

JP,
-- Alexander Widdlemouse undid his bellybutton and his bum dropped off --