Why can't we do Stealth kill in Survival mission

[CrimsonEye86]

Hi team,

first of all, thank you for the great update! The content was great, new warframe is awesome!

I discovered today that I can't execution move behind the enemies when in stealth/invisible abilities influence in any survival mission

It doesn't matter if I am fighting grineer, infested, or corpus, Fallen/Orokin,all the same problem. 

Was this intended or it's a bug?