I have seen that happening sometimes too.
Did you recognize what exactly happens and how that mangles your link ?
As PaulS points out, the button in the toolbar of the "deluxe" (or whatever it's called) editor pre-formats the link.
It assumes a link is no link if it doesn't start with "HTTPS://", so it "helps" you by adding that to the link, whether you did that yourself already or not.
I don't use that toolbar and just type out the codes while composing messages, and yet have seen that problem before once or twice.
I do try to do a preview before i submit messages with links or other special functions, so i can test those functions to do what i expected them to do.
But that will cast me from the bare editor into the 'deluxe' editor, and sometimes messes up the post.
So did how did you create your post, and when did you notice this problem ?