I opened the Software Boutique and clicked on Sound and Video and then after that opened I clicked on filters and the menu for filters did not drop down where you would think it would. I updated my laptop and then restarted and had the same problem. I have not seen it reported and I'm not sure how I would report it as a bug, if I need to report it at all.
EDIT: I did change my theme from Qogir Dark to Ambient-MATE-Dark and had the same problem.
Grr, it just so happens gir1.2-webkit2-4.0, which renders Welcome's pages had updated to 2.28.1 for security updates and clearly there is a regression since 2.28.0 
This affects other WebKit2 applications too, like GNOME Browser (epiphany-browser)
Good news, we spotted the bug report - it'll be fixed in a future update to the gir1.2-webkit2-4.0 package:
Fix came through in today's updates.
I've been running Ubuntu on a test machine and just got back into Mate and updated my machine. The Boutique problem that I listed above is now gone and working correctly. Thank you @layingback for filing the bug, which in a way turned out to be a duplicate mentioned above by @lah7 but I would have never known to look for that. Thank you Team Ubuntu Mate for your hard work.
