I found some weird behavior when viewing events and using category filtering.
When clicking the category items in the left bar repeatedly, duplicate ids will be added to the filtering in the URL.
These duplicates will not be displayed in the upper category bar, where the category will only be displayed once.
When clicking the "x" on that category in the upper category bar, the category will not be removed from the filtering.
This only happens if the category is not the only selected category for filtering, in that case the removal works as expected.