Imap Asynchronous methods: Deleting Message by MessageID

Is there any reason why the asynchronous Begin and End Fetch methods can only fetch based on sequence number and not also on the message ID, as synchronous Fetch can? Especially for parallel fetching and deleting it would be very helpful, as the sequence number is more ambiguous and seems to behave inconsistently, for example if I call DeleteMessage(1), the first message gets deleted, but if ExpungeMessages() isn't called right away, then next FetchMessage(1) still returns that deleted message, but, if you call another DeleteMessage(1), it will delete the second message, not the first one that was already marked as deleted.

This inconsistency might cause problems when trying to run Fetch+Del methods asynchronously in parallel using the sequence numbers, deleting different messages than intended as their indexing seems to change with every delete, but Fetch indexing changes only after Expunge...

Martin