Mailcore2 on Android storeFlags operation hangs

I'm trying to set the delete flag on a message, and when I run start() on the storeFlags operation, it hangs, and the emulator says the application has stopped running. Here's my code:

IndexSet set = IndexSet.indexSetWithIndex(message.uid());
IMAPOperation setDeleteFlagOperation = 
    MessagesSyncManager.singleton().session.storeFlagsByUIDOperation(
        "INBOX", set, IMAPStoreFlagsRequestKind.IMAPStoreFlagsRequestKindSet, 
        MessageFlag.MessageFlagDeleted);
setDeleteFlagOperation.start(this);

I've also tried using storeFlagsByNumberOperation() to create the operation with the same result. I've made sure that I pass in a valid UID, or in the case of storeFlagsByNumberOperation(), a valid sequence number. Can you tell me what I'm doing wrong?

via Chebli Mohamed