How to experience this bug properly:
1) Decide that you need a link to a Flow topic whose horrible URL nobody should ever have to type.
2) Copy and paste the link into VisualEditor.
3) Decide that nobody should even to have to read that dreadful URL. Maybe it should say something like "VisualEditor/Feedback topic on mediawiki.org". Copy that.
4) Select the link (carefully inside the blue boundary box). Paste (must be pasted, not typed!) the desired link label.
5) Hmm. That deleted my link.
6) Undo to get the unreadable URL back. Select the link (cursor in the middle of the URL) and click the 'Edit' button in the context menu. That's hopeless; there's no 'add a label' option, beause it's the whole horrible URL rather than [1]. Also, there's no way to convert it to [1], which means that using [1] as workaround isn't possible.
7) Select the horrible URL except for the first and last characters. Maybe I can paste it in the middle, and then backspace over the "h" (from the "https") and the last random character (in this case, "d").
8) Nope, that didn't work. That gets two copies of the link, separated by plain text: "h" (with the gibberish link), "VisualEditor/Feedback on mediawiki.org" (plain text), and "d" (with its own copy of the gibberish link).
9) Complain at the devs. Perhaps an unfortunate interaction between the new copypaste update and the link tool?
10) File this bug.
11) Make note to complain at @Quiddity again about how ugly those Flow URLs are.