When you control pick block a command block or a structure block, the item you get is just a default command/structure block and doesn't have any commands, data, names, or information of the block that you pick blocked.

How to reproduce
1. place a command/structure block
2. Put some info into the block (a command, a structure to load/save, etc)
3. Exit the interface, look at it, hold control and pick block it
4. The item you get will say (+Data), however when you place it, its just a default block with no info

Expected results
You should get an exact copy of the block you pick block, and what you place should have all the information of what you copied

I haven't experienced this bug with other items/blocks in the game, but I haven't tested them either. This could affect a lot more things than command/structure blocks!