While an infrastructure service such as mail really shouldn't run on Windows...
(run from an administrative prompt) show as owning process for port 143 when this issue strikes?
Running netstat -abno with IMAP unchecked in POA and POA now running does not show anything using 143
Is IMAP enabled at GWIA level?
Is the database level at 1810?
It might, of course, also be a plain defect due to some sort of timing issue.
If i understand this correctly you've previously had imap enabled on both POA and GWIA. On which ports? I'm asking because you mentioned "...not show anything using 143" which would, if GWIA's IMAP listener would be configured for 143, mean that we'd have an additional issue there.