Trying to type a word in brackets might lead to the disappearing of the opening brackets, no wikitext warning appears and no nowikis are added.
Happened to me twice in sandboxes,
see https://test.wikipedia.org/w/index.php?title=User:Elitre_(WMF)/tests&oldid=185158 and https://it.wikipedia.org/w/index.php?title=Utente%3AElitre_%28WMF%29%2FSandbox_VE&diff=62542564&oldid=62363821 ;
it didn't happen in https://en.wikipedia.org/w/index.php?title=User%3AElitre_%28WMF%29%2FSandbox&diff=582254513&oldid=581339890 and I also don't seem able to get this bug while VEditing ns0.
All tests under Chrome and Vector.