Same thing happens to me. Version 0.24.1 on Windows XP SP2.
The "autosave download queue" option is enabled and set to 5 minutes. (default setting)
[update] A tip given in the IRC channel worked for me: some anti-virus programs seem to interfere with the queue. This can be bypassed by adding the ABZ temp directory to the 'trusted zone' of your anti-virus. At least, that worked for me. (Kaspersky AV)