App duplicates lessons

[milan-codes]

Issue

I've stumbled upon the following problem in the Subjects fragment: When the fragment is opened for the first time, everything works just fine, BUT the moment users open the fragment for the second time (or just simply reload it), users face the following issue: the app starts filling in random circles with that blue-ish color as if there were lessons on that particular day.

Steps to reproduce

Let's say the user added two subjects, Calculus I and Databases, and a lesson to Databases on Wednesday. As soon as the fragment gets opened for the second time, there'll be a filled-in circle next to Calculus I's Wednesday as well.