You didn't use the "double-bar" syntax when you transcluded {{$:/_Menu/TopBar}}. It should be {{||$:/_Menu/TopBar}}, so that the current tiddler is in context.
Also, you have an unterminated <$list> widget at the beginning of the tiddler with a filter="[is[current]]", which will ALWAYS be true, so the $list widget does nothing except set the currentTiddler variable equal to... the value of the currentTiddler variable (i.e., the value is UNCHANGED by the $list widget action). Thus, this syntax is both unneeded and ineffective and can be removed from your template.
enjoy,
-e
P.S. I'm looking into the combobox problem you reported (how to set a value other than the selected tiddler title).