When attempting to use

/setblock x y z command_block 0 {DataTags}

or

/setblock x y z wall_sign 4 {DataTags}

, the command fails with this error:

[20:26:18] Data tag parsing failed: Invalid tag encountered, expected '{' as first char.

I have checked over the data tag multiple times, the only thing that seems to work is doing

/setblock x y z command_block 0

and then

/blockdata x y z {DataTags}

, which is hardly optimal for what I'm doing. The error has been reproduced with several different commands in different places in the world, all with correctly formatted data tags.