Cannot sniff Disassociation frames

Hello,

I am trying to sniff 802.11 Disassociation frames in wireshark but it seems impossible. In the filter expression I am using wlan.fc.type_subtype==0x0A but I don't see anything. I tried disconnecting a connected wireless client using the first time the normal windows disconnect options and the second time to shut down the wireless interface. Nothing... I even shut down unexpectedly the wireless interface in the Access Point but still the same result. Is something wrong in my filtering expression? I can sniff without any problem all other types of frames. I am using the ALFA AWUS036H adaptor in Ubuntu 12.04.

Kind regards