I think I was using the dropdowns although at the time I didn’t really worry about it. Certainly the dropdowns are commonly used here.
Its good to know it is a known issue at least. We are on Groupwise 6.5 and not likely to jump to 7.0 in the near future.
Meantime, I found a way round it by noting what the user had asked for (i.e. the type of Reply or Forward) and then canceling the event regardless (which stops the second call). I can then use Commander to replicate whatever the event was. Seems to work OK.
Thanks for you help.