nested @if/@else in wizard preprocessor not recognized?

I have a custom template wizard that uses nested @if conditions, here is an example:

@if "%PIMPL%" == "true"
private:
@if "%Internal%" == "true"
    Internal::%ClassName:c%Private *d;
@else
    %ClassName:c%Private *d;
@endif
@endif

The output when the "PIMPL" in the wizard is checked and "Internal" is unchecked (for a TestClass ClassName:

    Internal::TestClassPrivate *d;

This should not happen as the whole "PIMPL" block should be deactivated.