Hello,
I am using the following Kali Linux vesion:
3.7-trunk-686-pae #1 SMP Debian 3.7.2-0+kali8 i686 (kali-linux-1.0.5-i386.iso from the download site)

I have loaded this version on a Dell Latitude E6400 with the following WLAN adapter:
Intel Corporation WiFi Link 5100
In my system, this adapter is assigned wlan0

The following commands work with no issues:
1) iwlist wlan0 scanning = produces list of available networks
2) airmon-ng start wlan0 <channel> = starts monitor mode on wlan0 on specified channel
3) wireshark = launches wireshark. I am able to start capturing in wireshark and the packets are displayed.
4) airmon-ng stop wlan0 = takes wlan0 out of monitoring mode

After inspecting some WLAN captures in wireshark, I noticed that the WLAN adpater does not capture any packets that have 40MHz channel bandwidth.
According to the Intel website, this WLAN adapter does support 40MHz operation. See link:
http://www.intel.com/products/wireless/adapters/5000/

Can someone please help?