Thanks for your quick reply, Tobias!
I contacted UpSolution (the creators of the Impreza theme). This is their reply:
Unfortunately, this is a bug. We’ll fix it and will let you know once the fix is published.
As a quick workaround, you can turn off the checkbox inside the table settings: “Enable horizontal scrolling, to make viewing tables with many columns easier.” (the last checkbox in the list). It seems to be the one causing the conflict.
Since this is a per-table setting and my site uses over 120 tables, I have decided to just accept the weird look for now and hope that UpSolution releases the fix soon.
Thanks for making this great tool!
