The difference here could be related to the fact that we do not have a driver for Windows* 8.1 at this time. Perhaps using Microsoft* driver may give different results.
I went into
Device Manager > Network Adapters > Right Click on Intel Centrino card > Update Driver
Browse My Computer for Device Drivers > Let Me Pick
I had many drivers that had (Intel) at the end and one with (Microsoft)
I will try that for a while and see what happens.
Here is what I had to do on a Lenovo T430 with Centrino Wireless-N 2200 adapter and Windows 8.1 x64:
Since my laptop has BIOS options for WiMAX and Wireless WAN, I entered the BIOS and went to Security and the I/O Port Access and disabled the WiMAX and Wireless WAN options as I do not use either.
Go to System screen and choose Device Manager
Right click on the Centrino Wireless-N 2200 and choose Update Driver Software
Click on Browse my Computer for driver software
Click Let me pick from a list of devices...
Select the Intel Centrino Wireless-N 2200 (Microsoft) entry and follow screen to complete install
Right click on the Wireless-N 2200 adapter again and choose Properties
Verify driver (after all Windows updates)
Click on the Advanced tab
Select 802.11 n Mode and set to Disabled
Select Ad Hoc QoS Mode and set to WMM Enabled
Select Wireless Mode and verify it is set to 3. 802.11b/g
Click on the Power Management Tab and uncheck box Allow the computer to turn off device...
Where this is a development machine, I also adjusted the power settings as it is connected to a docking station and on all the time.
Wireless Adapter Settings set to Max Performance for Both
Sleep settings all set to Never for all sub components
PCI Express - Link state setting both set to Off.
Hope this might help your case but I have had no other issues on my Lenovo.
But I can't see 802.11n Mode in advanced tab. I'm using intel dual band wireless-ac 7260, windows 8.1, and updated to the latest version driver.