Watchlist removes element with comma in name when adding new element

Steps to reproduce:

• create a new page witha comma in the name, say Sandbox.a,b
• add this page to your watchlist
• add another page, say Sandbox.WebHome

Expected: both Sandbox.a,b and Sandbox.WebHome and in the watchlist
Observed: only Sandbox.WebHome

The problem is that when adding page commas only get escaped in the element added, but not in the elements already present, while these get unescaped when loading the list.