Ok I have broken the Parser by using embedded {CALL:x} within a {SETTING:x} command. It does not work in either RULES or Widgets.
This will break:
[=F(TN('{SETTING:AUDcount_{CALL:Name.Id('{SETTING:DEPARTMENT}')}{CALL:Name.No('{SETTING:CURRENTTERMINAL}')}_100d}')*100,'0.00')]
A single {CALL:x} will also break it.
[EDIT]
I have got around this by the use of Local Variables they are created from Form Editor Widgets. So now just FYI.