Can confirm, even in Snapshot 14w20b. I was trying to make a flying machine that teleports the player with the flying machine. It seems that whenever the player jumps around or sprints, the glitch shown above will occur.
Updated:Sorry for any confusion. Signs only disrupt the signal if on the same face of the block as the item frame. Signs on top do not disrupt it.
Can confirm, even in Snapshot 14w20b. I was trying to make a flying machine that teleports the player with the flying machine. It seems that whenever the player jumps around or sprints, the glitch shown above will occur.