It seems to be a weird fluke.
Wayback machine links seem to have two components to them (the link to Wayback and the original link).
Perhaps this has created some sort of conflict in the linkable text facility but as you can see the link on it's own works fine.
***UPDATE***
It was my own stupid fault.
Just noticed I tried to paste a link into a link causing the conflict to happen.
Sorry but even after years of using these forums I'm still learning new things.