I think this is OK, because the bras and kets do not have any labels associated with them, and the they don't need it either if one creates a tensorproduct spaces of operators and states. Like in the end of this example:

http://nbviewer.ipython.org/gist/jrjohansson/8017549

In my opinion it is better to work with tensor products of operators and states than to use labels to select which operator which ket should act on (at least in my use-cases)