[TxMt] Web preview disappears?

I know it's probably something obvious I'm not doing, but I'd really like to be able to preview an HTML document in a project while editing a linked CSS file. Every time I open a preview on the HTML document and switch to the CSS file in my project, the web preview closes. Is this normal?

I've been doing fine with using the "Refresh open browsers" command and split off commands to shift-refresh firefox and exclusively refresh Xylescope, but having the instant feedback in the web preview would be great, especially when combined with the current ability to pipe through your PHP installation.

Thanks, Brett