odd forum error

On my Chaos Fields page in the Forums, animated gif links included as Image links fail, they used to work:
https://www.filterforge.com/forum/read...MID=163433
The reason is that the image link is changed from a http link to a https link in the posts towards the bottom of the post.

The Image link in the last post that fails is:
http://duim.com/animate/squirclesanimated-test11.gif
... but it is changed to a secure link:
https://duim.com/animate/squirclesanimated-test11.gif

It fails in Firefox and Edge on the Mac, but works correctly in Safari. Odd, don't know if anything was changed on the Forum site, it used to work.

UPDATE: I bought a SSL certificate, so it now works, but the IMG link in the forum messages should not switch from http to https. FWIW