<<still wondering>>

I'd never heard of the usage you found, but I love it, because I do it all the time. Say you have chop and mince different ingredients to be added separately to the dish. You prepare the ingredients and cover them with a bowl to keep the cockroaches out...er, keep them fresh. But -- do you 'whelm the bowl' or 'whelm the ingredients,' or do you 'whelm the bowl' but 'overwhelm' the ingredients?'