Here is how to reproduce it:
- create a block with name "test" (with any object, doesn't matter)
- delete this block
- create a block with the same name "test" again
=> it will complain that a block with this name exists already which isn't the case.
You need to close and open the file to be able to create the block with the same name again.
Duplicate of [#463]
Related
Bugs:
#463