Impossible to move messages to trash when overquota

[Stefano Tabacchiera]

Hi all,
my box is running cyrus-2.1.11 and I set up quota for my users.
When someone is overquota, it's impossible to MOVE messages to Trash and 
then delete them. The only way is to NOT use Trash, mark messages as 
deleted and then expunge.
Question is: why ???
Is there a workaround for this?
Almost all of my users use 'move-to-Trash->then-empty-Trash'. So I dont 
want to force them to change.
Any clue?

Thanks all.