Certain countries won't let a visitor enter if they have a passport stamp from certain other countries.
One case is Azerbaijan which will not permit you to enter if you have a stamp of Nagorno-Karabakh.
In some parts of the world with problems like this the place with the controversial stamp may put it on a separate piece of paper rather than in your passport. Reportedly Cuba will do this for Americans for instance.
Does anybody know whether Nagorno-Karabakh will do this?