Version:           KPilot 4.6.0 (using KDE KDE 3.5.3)
Installed from:    Ubuntu Packages
OS:                Linux

I have used KOrganizer successfully for months.
Today for the first time I synced my newly acquired Treo 650 using KPilot.
Ordinary events transferred to the Treo OK.
Weekly recurring events transferred to the Treo OK.
The following recurring events transferred at the correct time but on the next day:
The last Tuesday evening of every month event showed up on the next Wednesday evening.
The 4th Tuesday evening of every month event showed up on the next Wednesday evening.
The 2nd Tuesday evening of every month event showed up on the next Wednesday evening.

Here's an example of the last Tuesday of every month event:
BEGIN:VEVENT
DTSTAMP:20070328T174044Z
ORGANIZER:MAILTO:
X-PILOTID:13414488
X-PILOTSTAT:0
CREATED:20070124T075039Z
UID:KOrganizer-2063942894.125
SEQUENCE:1
LAST-MODIFIED:20070328T173948Z
SUMMARY:OCCA
CLASS:PUBLIC
PRIORITY:5
RELATED-TO:libkcal-530135244.762
RRULE:FREQ=MONTHLY;BYDAY=-1TU
DTSTART:20070130T180000Z
DTEND:20070130T210000Z
TRANSP:OPAQUE
END:VEVENT

Here's the 2nd Tuesday event that showed up on Wednesday:
BEGIN:VEVENT
DTSTAMP:20070328T174044Z
ORGANIZER;CN=Joe Mepis:MAILTO:
X-PILOTID:13414603
X-PILOTSTAT:0
CREATED:20070102T102320Z
UID:KOrganizer-439045704.708
SEQUENCE:0
LAST-MODIFIED:20070328T173952Z
SUMMARY:TVLinux
CLASS:PUBLIC
PRIORITY:5
RRULE:FREQ=MONTHLY;BYDAY=2TU
DTSTART:20070109T170000Z
DTEND:20070109T203000Z
TRANSP:OPAQUE
END:VEVENT