This bug applies to both singleplayer and multiplayer servers.

What I expected to happen was...:
Copy a command block in creative mode while holding CTRL to get its NBT data

What actually happened was...:
The command in the block saved, but the "conditional" setting changed back to unconditional

Steps to Reproduce:
1. place down a command block and open it
2. change the "unconditional" setting to conditional
3. copy the placed command block to your hotbar (the default keybind is middle mouse button) while holding CTRL to fetch the NBT data of the command block you placed down

4. Place the NBT command block down. It will be set to "unconditional" despite having changed it prior.