Speed Guide increases my chosen port by 1

[stumblingblock]

weird problem. everything works fine for awhile, then for unknown reason, when i go to Options:>Speed Guide, utorrent has increased my chosen port by 1 (ie if my port was 12345, it will show 12346). if i wipe out the chosen port, put in something else, wipe that out, put back my chosen port, it will SOMETIMES correct, but not always right away. anyone else seen this? whats going on?

(edit) downloads seem to work ok in any case. if i increase my chosen port by 1 to match Speed Guide, (eg 12345 to 12346) it will increase by ANOTHER 1 digit.

router WRT54GL Linksys

utorrent 1.8.5

this has been an occasional problem for a LONG time, it comes and goes.

(edit again) in response to question from DreadWingKnight below,

uPnP is enabled

[DreadWingKnight]

UPnP enabled?

[Switeck]

Try disabling both UPnP and NAT-PMP in uTorrent.

[stumblingblock]

Disabling UPnP seems to have worked.

thanks