I've done some testing of this and from what I can see it looks to be only partially fixed. Here's my test:
Spam zombie eggs until you get a jockey (I used a dispenser hooked to a clock) into a sealed chamber. Make it with glass so the zombie doesn't take suffocation damage when the chicken is too close to the wall, cover it with opaque blocks to prevent sunburn.
Teleport 128 blocks away and wait about 30 seconds
Teleport back, and I found that the chicken and zombie were both gone (hard to say if they despawned or glitched into oblivion somehow).
Repeat the test, however instead of teleporting away, walk 128 blocks away and walk back. 9 out of 10 times, the zombie was gone but the chicken remained.
Assuming the intention was for both chicken and zombie to despawn, it doesn't always work as intended.
I've seen this in a circuit I currently use. This is using a wooden button, however I have also seen this occur with a stone button. The sounds line up with the shorter pulse as well, playing the second "click" sound more quickly than usual. As for the length, hard to say, maybe describing the circuit path would be helpful? The signal travels through 5 meters of redstone wiring to activate a dispenser, then through a repeater set to a 3 tick delay to a falling edge detector using a repeater lock which powers the dispenser when the pulse ends. The pulse generated normally from either a stone or wooden button is long enough to activate the dispenser twice with that circuit. The shortened pulse is enough to make it through the 3 tick delay repeater and "charge" the falling edge detector but the pulse doesn't stay on long enough for the falling edge to activate the dispenser a second time. This has happened twice in the past 100 uses of the circuit.
Just tested it, yes it is still an issue. In one instance the chicken pressed itself into a corner which suffocated the zombie, in another instance the chicken rotated itself to face away from the wall without moving away from the wall, which placed the zombie in the wall enough to suffocate it.