If you haven't done so already, would it be possible to submit a Tasks & Lists issue report via our support system?

Please select the issue that you're experiencing from the list on the left, and follow the steps shown. If your issue isn't listed, just click on "I'd like to report a new issue" on the left.

Your report should provide all the info that we need to investigate further, but we'll be in touch via email if we require any more details.

Thanks!

Same thing is happening to me, but not just for the Work tab. It seems to be true for any of the subsets of the Tasks list.