The TextBox controls with a MaskedEditExtender associated, doesn't allow to remove the values introduced (with the del or supr keys) in Webkit based browsers (Safari and Chrome).
Comments: there is a related issue on code.google: http://code.google.com/p/chromium/issues/detail?id=3341
Comments: there is a related issue on code.google: http://code.google.com/p/chromium/issues/detail?id=3341