Latch bolt stuck inside door jamb
This isn't a recent post but I thought my experience might help someone. I had a similar situation where the knobs were off but the latch wouldn't release. It seems the transmission plate came unattached from the latch somewhere inside the mechanism, so sliding it back with a screwdriver did nothing. 

I tried to take the door off the hinges but it wouldn't budge even with significant force. I have an older door with a 5 inch backset so the latch was very long and perhaps helped to hold the door tight even with the hinge pins out. 

Ultimately I got out my Dremel multi max with a wood/metal blade attachment, slotted it between the door and jamb at the face plate and sawed through the bolt. I really didn't think that would work, but the cheap Kwikset bolt was partially hollow and didn't provide a lot of resistance. If you go this route you'll want to dig the cut piece out of the bolt hole with a screwdriver and not your finger, as it will be quite hot from cutting through.