Shit's too fast, the combo is fully done by the time you stand up. Literally just hit shoot > melee > nade on your keyboard as fast as you can. Dunno if mashing wraith form or something gets you out though.
Not saying it's busted, just saying it's really and kind of unexpected.
Edit: Here's a hilarious gif going around of it happening to somebody https://twitter.com/100ryun/status/753200228178599936
Oh damn lol.