I noticed that when I create an input from a pin with a default, it will show that default in the tooltip, but when I open the middle-mouse menu, default shows as empty.
When you click in the default once, it will now have “” (empty) as the default.
Tested in 6.6 and 6.7-0238
It seems to be the case with several data types, not just strings. Also noticed it with booleans.