Details...
I am using DCS version 1.2.16.39472 on Windows 7 and playing the KA-50 training mission "Datalink and Wingmen" from BigfootMSR.
Disabling "EASY COMMUNICATION" and using RAlt+\ only works if you also copy the training mission from the KA-50 training folder and put it in your /username/Saved Games/DCS/Missions folder and open it from the mission menu.
I also noticed that even though I have labels turned off, they still appear when I play from the training section. However, when I play from the mission section the labels are off. It appears that when playing from the training folder there are some gameplay settings that get turned on.
Dare I speculate...
It looks like the real issue is that easy communication does not work correctly. But, the problem is compounded because even if you turn off easy communication it seems to still be on when playing from the training menu.