Around 17 seconds into episode 3 of Re-Kan!, there is this weird window (as in GUI element) from Windows Vista or Windows 7 on the wall of the classroom.
Another screenshot at around 07:22 in episode 1, showing the window in the lower right corner.
Looking through all 3 episodes which are aired so far, the charts and the weird window are consistently animated. While the animation is consistent, the choice of article to place on the wall is still weird. The window element looks completely out of place.
Is this an animation mistake?