[Wikitech-l] subst: and Parser::preprocess not sending correct frame to tag extensions?

I'm not sure if this is by design, but it seems when using a tag extension inside of a template, the tag extension is not passed the correct frame information about the template when using subst: or Parser::preprocess

For example: The contents of Template:Test are:

<SomeTagExtension> {{{1}}} </SomeTagExtension>

When using {{subst:Test|Hello World}} You get

<SomeTagExtension> {{{1}}} </SomeTagExtension>

Even if SomeTagExtension is correctly using $parser->recursiveTagParse.

It seems the $frame value does not contain the template variables when using subst or preprocess. The frame object type is PPFrame_DOM instead of PPTemplateFrame_DOM.

Am I doing something wrong, is this by design, or is it a bug?

Thanks Andrew