In a button this seems to be never true:
@if:Set VIEWPANE=off
Interestingly, inverting helps:
@if:!Set VIEWPANE=on
That works as expected.
A little demo:
// @if:!Set VIEWPANE=on
@if:Set VIEWPANE=off
Set VIEWPANE=on
@if:else
Set VIEWPANE=togglelayout
P.S.: Testing for Set DUAL=off
works fine, e.g.
@if:Set DUAL=off
Set DUAL=on
@if:else
Set DUAL=togglelayout