Dec 20 2016
Dec 17 2016
I'll put all my addons and Wikipedia gadgets here so that people can see whether there is any correlation, although I'll be checking through them myself later once I find a reliable way to set cookies to trigger the issue again. If it seems like too much effort, nobody needs to do anything with this list, but just in case someone spots something known or obvious...
Dec 15 2016
Thanks for interpreting that, @Anomie. I tried reproducing the problem using scripts like this one and httpbin, but in each case it was possible to save more than 16 cookies. So if it is something in my browser, it is not affecting every site. I will investigate more later, to see whether some browser extension or Wikipedia gadget may be the cause, as I do have a few of each enabled.
Dec 9 2015
Seems to be behaving correctly for me now. Should probably wait a bit more before closing?
Nov 30 2015
For me, the first one linked above in zhuyifei's comment looks like this:
Nov 27 2015
It seems this image is also affected: https://commons.wikimedia.org/wiki/File:Glasl's_Model_of_Conflict_Escalation.svg