The best way is to follow the instructions on the Sage Trac and get an account to open your own ticket. That is best because then you start becoming a named and invested member of the Sage team!
In fact, it's possible that the bug is already reported; you might as well do a search on the Trac (or a Google search with that site as the site) for whether something similar has been reported. The person who wrote the MILP tutorial is very responsive, so I'm sure it will be fixed quickly if it hasn't been already (there was recently an upgrade to that very thing...).
However, you could also just edit your question and show the error (be sure to use the 101010 button to make code look ok) and someone could report it.