Still happens in 1.7.2
Also, compactness is kind of important in an compact 3x3 door 😛 I have yet to find a work around, and it seems to be only a few specific coordinates (I got it working at a different location, with the same Y value), Perhaps it is related to MC-11193 in some weird way? Still an annoying bug as that's the most convenient place to put the door. I also tested it on a friends server, in four different locations, one of them extended bottom piston, the other three acted as expected.
MC-29430 is similar, except both pistons aren't extending, that was an error with me building it during later testing. only one piston extends, the problem is whether it is the top or bottom.
No, that was never mind to my previous comment. sorry.
Nevermind... I just built it wrong, but the bottom one is extending at Y=65
Okay, now i'm doubting myself... tested at Y=65 and they both extend/retract in rapid succession (bottom exends, bottom retracts top extends, top retracts)
Tested at Y=56, BOTTOM piston extends. so it seems Y=57 is the crucial height
That's very weird, I just tested at Y=58, and the TOP piston extends... I'll continue testing
Sorry, I am unable to test this on newer versions due to loss of my pc.