When viewing questions in one of the main tabs, changing the number of questions-per-page preserves the current page number in the URL. This makes little sense as, for example, the 5th page of 50 items is nowhere near the 5th page of 15 which I was just browsing.
In addition, if I'm viewing 15 per page and I'm at a high enough numbered page (such as the last page of items), when I change pagination to a higher number, I arrive at an empty page well beyond the last page which contains content.
A suggestion such as the one in this feature request would handily deal with that situation, but at the very least, when changing pagination the page number should probably be simply omitted from the URL. Jumping back to page one makes at least as much sense as jumping to the same-numbered page at a different pagination.