fill ~1 ~ ~1 ~4 ~ ~4 minecraft:stone 0 replace minecraft:command_block works
fill ~1 ~ ~1 ~4 ~ ~4 minecraft:command_block 0 replace minecraft:command_block doesn't work
/fill ~1 ~ ~1 ~4 ~ ~4 minecraft:brewing_stand 0 replace minecraft:air
doesn't work
Edit: Found a duplicate of this that is openned & confirmed (didn't see this was duplicated) so ignore this.
I have this bug too. I was going to make a easy command block placement system but it cannot be made because of this glitch. Here is what I was doing:
/fill ~3 ~3 ~3 ~-3 ~-3 ~-3 minecraft:command_block 0 replace minecraft:bedrock
When using the replace method of /fill it doesn't accept (I think) anything using tile entities. I test the command above but with minecraft:chest & it also fails:
/fill ~3 ~3 ~3 ~-3 ~-3 ~-3 minecraft:chest 0 replace minecraft:bedrock
Both fail with: Data tag parsing failed: Not a valid tag
Hopefully this can be fixed in the next snapshot because I really want to make this system.