This is an unfortunate "working as intended". It significantly increases the difficulty and size of toggle switches, and causes unexpected behaviour when moving between versions.
I can confirm that driving the last stage of your input chain with a redstone block on a piston does work as a fix (with as many relays running into the redstone block piston as you need). This leads me to believe it's a problem with the way piston timing and redstone timings interact.
Siphio
MCPE-15793
This is an unfortunate "working as intended". It significantly increases the difficulty and size of toggle switches, and causes unexpected behaviour when moving between versions.
I can confirm that driving the last stage of your input chain with a redstone block on a piston does work as a fix (with as many relays running into the redstone block piston as you need). This leads me to believe it's a problem with the way piston timing and redstone timings interact.
Still a problem in 0.15.2
Still broken in 15.4.