Steps to reproduce: Make your browser window very small. If there is not enough space at the bottom, the popups open to the top. Then the first 2 popups overlap with skin elements.
This might be an upstream #OOUI bug, or simply a z-index missing.
See bug report [[ https://www.mediawiki.org/wiki/Topic:Ud4mm7woz1544yt5 |here]].