https versus http - messes up thread framing. Help?

[K-fab]

Okay, here are two examples. The top entry is with https, the bottom is with http

https versus http issues

Coding is as follows (obviously w/o the spaces) - and this is the only line in each entry.

Top entry, that has the messed up framing:
[URL = "https://www.youtube.com/watch?v=M2NKa48M-p0"]To the Moon![/ URL]

Bottom entry, w/o the s:
[URL = "http://www.youtube.com/watch?v=M2NKa48M-p0"]To the Moon![/ URL]

The s seems to be the culprit, but why?

You can see that it splits the post above the signature line with the s in https, while w/o the s all is correct.