I need som tips from the wireless community with a challenge I have

Background
I was preparing a blogarticle about transmit power mismatch impact on datarates when I discovered that my Windows client was transmitting  dataframes towards the AP with 2 spatial stream (mcs 8-15), while the AP only transmit with 1 spatial stream (mcs 0-7) toward my client.
No matter how near those stations was each other the same transmit-pattern happened

Clientdata
The client is a Lenovo X-320 with Intel advanced-n 6205 wireless nic. Drivers version is 15.18.0.1 from 30.april 2015. Window 10

Wireless infrastructure
I have tested the client against Cisco 2602i and Cisco 2702i accesspoint both in centralized, flex connect and autonomous mode. And towards different network, both our production and two different wlc-labnetwork. And with WPA2 Enterprise, WPA2 Personal and Open authentication

Other moments:
– The wlc has almost default configuration except TPC, level 3
– The RSSI on both client and AP/WLC is appr.  -60dBm
– No CCI, tested on 5GHz, channel 36, 40 and 44
– 20 MHz channel

Examination of frames
I have studied management frames, association request and association response, and both enables mcs 0-15 under HT Capabilities element, RX Supported Modulation and Coding Scheme.
And I can’t find anything else that should tell me that the AP only transmit mcs 0-7

Wireless NIC driver
I have find a nic-driver with version 19.70.0, but the client refuse to install that. It says that 15.18.0.1 is the best nic-driver
A google-search on that wireless-nic only displays problems with installation

So the condition should be good enough so that the AP could transmit with 2ss
When I test with a 2ss tablet (iPAD), both stations transmit with 2ss

Question to the wireless community
– Is this a common problem with that wireless nic (Intel advanced-n 6205)?
– In which wireless frame and information element  should I find that this happens?
– Any solution?