The date member of the ENVELOPE is the field-contents of the Date: header. IMAP makes no representation that this is in RFC 2822 format.
Consequently, I agree with your assessment that OE is engaging in bad behavior and you should not mess with the data. I see no reason to parse and reconstruct the date; indeed, you may cause more harm than good by doing so. -- Mark -- http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
