/fill x1 y1 z1 x2 y2 z2 [tile entity] replace [block] gives parse error

The problem occurs if running via command block and normally via chat.

Steps to reproduce the problem:
1. Place a command block with fill ~ ~1 ~ ~ ~1 ~ minecraft:unpowered_comparator 3 replace minecraft:diamond_block
2. Place a diamond block on top
3. Activate the command block

Expected behaviour:
The diamond block gets turned into comparator

Actual behaviour:
Error message
Data tag parsing failed: Invalid tag encountered, expected '{' as first char.

Additional information:
The command fill ~ ~1 ~ ~ ~1 ~ minecraft:unpowered_comparator 3 works.
It also works with block other than unpowered_comparator.
According to the wiki the command expects fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> <dataValue> replace [replaceTileName] [replaceDataValue].