MailThreadManagerImpl can cause repeated OOMEs if inbound message has corrupt References header

We have an OD instance that is repeatedly OOME'ing due to this List in MailThreadManagerImpl.extractMessageIdsFromReferences() accumulating many millions of Strings.

Click for heap dump and OOME event info.

Looks like extractMessageIdsFromReferences() is broken if the argument doesn't include a closing angle bracket — which, as far as I can tell, violates rfc2822, but does seem to be occurring in production in this case, where the value is: <20130120014306.G

With such a value, the List fills up with empty String Objects until the instance OOMEs.