I haven't had another opportunity to check out the workbench again since then. I'll try again when I get the time. What I did was interact with the workbench and then click on my rifle to check out what mods I can attach to it. I currently did not have a mod for it. It was then that I could not "Esc". I was stuck with the Rifle image on the center with the empty slots on the left. The bottom text said Press "Esc" to exit. But hitting Esc and all other buttons did not do so. I game was not frozen since i was still able to rotate the rifle with my mouse.