Cisco Firewall :: ASA 8.2.4(4) Seems To Be Dropping Valid TCP SYN Packets?

We have a setup with a MS-TMG - ASA (8.2.4(4) in routing mode) - (internal) Router - FWSM - Router - Exchange with NLB.  We have now the problem that IMAPS is not really working through this setup. It works from internal (without ASA and TMG inbetween), but not reliably through the internet. There is a rule on the ASA which permits the ports from the TMG to the Exchange NLB address.We opened a case with Microsoft and they told us that not all tcp-syn packets are received by the Exchange server which were sent by the TMG.Thus I sniffed on the ASA with a packet capture and indeed, a lot of syn packets were on the interface to the TMG, but not anymore on the interface to the internal router.This ASA also filters all other internet<->company traffic, so there's a lot of stuff running.
 
Maybe it's dropped in the ASP, or is the capture maybe not valid?Here the show asp drop:

ASA01-Internet# sh asp drop
Frame drop:  Invalid TCP Length (invalid-tcp-hdr-length)                                  1  Reverse-path verify failed (rpf-violated)                                  319  Flow is denied by configured rule (acl-drop)                            477077  First TCP packet not SYN (tcp-not-syn)                                   10212  TCP data send after FIN (tcp-data-past-fin)                                 41  TCP failed 3 way handshake (tcp-3whs-failed)                               824  TCP RST/FIN out of order (tcp-rstfin-ooo)                                 1419  TCP SEQ in SYN/SYNACK invalid (tcp-seq-syn-diff)                             6  TCP SYNACK on established conn (tcp-synack-ooo)                              1  TCP packet SEQ past window (tcp-seq-past-win)                              821  TCP invalid ACK

[code]....