I was thinking about this last night when I should have been asleep. Anyway, I checked Fowler this morning (proper book, not online or Kindle!) and now I’m more-or-less sure of the usage. Here is what Fowler has to say (direct quote)
hang (verb) Use hanged as pa.t. and pa.ppl of capital punishment and in imprecations; otherwise hung. The distinction goes back ultimately to the existence of two OE verbs … hung became established in literary English in the late 16c., with hanged largely restricted to the sense ‘kill by hanging’ and in the imprecations of the kind I’ll be hanged if I’ll do that. In practice, a wide range of writers use hung in descriptions of executions. this use is not erroneous but just less customary in standard English.
I hope that clears it up for you! I still like to use hanged instead of hung – it annoys some people but that’s OK!
The New Fowler’s Modern English Usage. Third edition (1996). Oxford
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