If an error occurs while updating alternatives (e.g. update-alternatives script 
was called to create a symlink in nonexisting directory) only error message
appears about this particular error, but nohing says that all other alternatives
since the moment error occured will be left unprocessed. In effect, broken 
alternatives appear in the system, and there's no direct connection with erroneous
package so it won't very easy to trace an error.

Simple way to resolve this will be to add after a message about real error a
warning message that "all subsequent alternatives will be left unprocessed".