Steps to Reproduce:

1. Find or make an area with a specific version of a block you'd like to replace and another version of the same block that you don't want to be replaced. ex) upside-down cobblestone stair and upright cobblestone stair
2. Execute a fill command with the coordinates of the location you had made/found and use a block state tag to select the one version of the block you would like to be replaced with another block of your choice. ex) /fill <from: x y z> <to: x y z> obsidian [] replace stone_stair ["upside_down_bit": true]

Observed Results:

What I found to happen was that both of the blocks got turned to obsidian even though it was only supposed to replace the upside-down one. The message that was shown after the execution of the command was "2 blocks filled".

Expected Results:

What I was expecting to happen was for it to only replace the block with the same block state value as input, leaving the other untouched.