Hi, sorry for the slow reply. There is a strange problem where sometimes the classname is not stored. I plan to upgrade this to the new method that hazelnut introduced in his items mod and that should hopefully squash this bug.
In the meantime, if you go into your savedata.txt file, and search for Telescope, you will find the section that descibes the telesope. Look for the line that reads "classname" and change to
It might appear twice in your savefile, just make sure that the class name is telescope and that should enable the functionality.