The multiple panes feature is great, but at the moment the sessions are sized to the dimensions of the RDTabs window and not the pane in which the session is running. Would it be possible to have the sessions resize themselves on connection so that they fill the pane they are in?

What you want is "fit to tab pane" display mode, which is on the "Display" tab in the Remote Desktop Connection Properties. "Fit to application window" is default, as you noticed. You can change this for all sessions by editing the Default Connection Properties in the Tools menu. You can change it for all saved favorites by "Batch Editing" favorites under the "Manage Favorites" menu item in the Favorites menu.

Let me know if this resolves your issue!

That's the one - missed it completely. Thanks 🙂