Specifically when you open the crafting menu for the (green) rares and select Fuse delayed grenade. Then move your mouse over to the items icon so that the pop up menu with the stats appears, and then close the screen with that pop up menu still there the entire game freezes with that pop up menu unable to be closed, you can select a few thing like the chat box and highlight a few thing on the screen but you cannot close it. I tried it twice just to make sure it was not a random fluke.
This is my first bug i have found.
Keep up the great work Neocore! *Two thumbs up*
"Venerate the immortal Emperor!"