Very interesting stuff!!!!
Interestingly, Tank, generally quite good and VERY good around people and other dogs, has an absolute loss of brainpower if he sees balls (the rubber kind

), we are always careful to avoid children playing ballgames, as you can guarantee Tank will be in there like a lunatic. Balls at home will be played with until they die, it generally doesnt take long.
Piper, also very well socialised, an absolute pleasure to have off-leash, cannot bear Jack Russell terriers Off she'll go like a speeding bullet with the JRT in full flight ahead. She is actually ok if THEY are on leash, then they dont worry her, but an off-leash JRT is like a red flag!
Ruby .... doesnt care about anything much, other than food, she's cool, man, really cool........
I've just realised I'm totally off-topic .... my point really, was I wonder if Tank associates rubber balls with some puppy trauma, he was born in the SPCA and was re-homed twice before he came to us at 6 months, poor lad.