After reverse pickpocketting Madesis' Ring on Brand-Shei, and watching him be marched away by the guards, Brynjolf instructs the player to go to the Ragged Flagon via the Ratway. If you exit this conversation via the TAB button instead of clicking through (it seems), chance of this quest stage not ending properly. If the glitch occurs, after entering the Ratway, Brynjolf spawns from the Ragged Flagon door and starts repeating his "come all" distraction pitch dialogue and walks all the way to the Ratway exit into Riften. He then goes back to his spot in the market and all of the marketplace NPCs will freeze in place around him. He then stands there and won't let you proceed with the quest. It seems to be due to the marketplace distraction script not ending properly, or something.

I solved this on PC by typing "resetquest TG00" and then "setstage TG00 30" in the console. Talk to Brynjolf after doing this and you get another shot at the dialouge that's meant to clear his marketplace distraction script.

Hopefully Bethesda can fix this and prevent it from occuring altogether in the next patch.