We have an E Series Tost (E85) mounted in a very deep, narrow nose tunnel. It has a single closing arm that pivots up. The lower, fixed arm has a channel that the ring will rest on w/o load. Under a no tension condition (e.g., slack rope and/or glider in a 0 or slightly neg G such as in a kiting-recovery maneuver; plus the positive air flow in the tunnel at ~70mph) could possibly result in failure to release. Might test this at altitude.
https://www.dropbox.com/sh/gs2fi5dij...vBmNY_GNa?dl=0

I can imagine that in some kiting incidents where the glider lowers the nose and creates rope slack (thereby temporarily unloading the tow plane's tail), taking up the slack could produce a sudden secondary pull up on the tail, making things even worse. The upward momentum of the tail would then require more elevator input than might be available.