Not decrypting both sides of the DHCP handshake

Hello.

I have AirPcap/Wireshark running on windows (both xp-32bit and 7-64bit).

I need to capture the DHCP handshake in order to get further with the support desk of two wireless AP vendors (how far down the rabbit hole am I? A long way :)

I need to solve this as the WiFi module in the product we are developing doesn't always complete the DHCP handshake with certain AP vendor's equipment, and their response is "show me one where it works".

I can successfully enter encryption information into wireshark and for the most part it seems to decrypt packets happily.

The problem I have is that while wireshark decodes the DHCP discover/request side of the handshake, it will not decode the DHCP offer/acknowledgement. I can see the wireless AP send the 802.11 ack frame, and I can see it send packets (which must be the offer/ack), but wireshark does not decode them.

I know the DHCP handshake is working since I get an IP address and can see on the AP that the IP address is allocated to my MAC address.

Wireshark also quite happily the decodes the ARP request and the reply without any problems. Which is the strange bit, why can it decode a packet received literally two packets later?

Why will it not decode the AP's DHCP responses?

I have tried to capture this for 4 different AP vendors that work, and in all cases I cannot get the full DHCP handshake.

I have also tried to do this at my lab bench and now also at home (where the "air" is rather more "quiet" :)

I have a capture file if that is of any use.

Sorry if this has been asked somewhere else, I have searched high and low, but cannot find anyone else mentioning this problem. Any help greatly appreciated.

Thanks in advance,

Bryan