Another query regarding expected transclusion behaviour:

Should the markup below pass the contents of TranscludedPage as a parameter to TemplatePage? For the specific template I'm actually using it seems to be calling TemplatePage with something like the literal parameter "{{:TranscludedPage}}" but then splitting up this token so that the final "}}" appears after a header break inserted by the template. Bug or just something that's not supposed to be possible?

{{TemplatePage|{{:TranscludedPage}}}}