Chainging bobber's NBT with a command block doesn't give a redstone pulse

Executing an entitydata command on a fishing rod's bobber in a command block doesn't give any redstone signal through a comparator

1) Type the /entitydata command in a command block with as selector @e[name=unknown] (is the bobber).
{My command was execute @a ~ ~ ~ /entitydata @e[name=unknown,r=5] {CustomName:"GrapplingHook1",CustomNameVisible:0}}

2. Attach a clock and a comparator to the command block

3. Use a fishing rod.

No signals come out of the comparator.