I'm curious what you use this for. When PTC first introduced the pinned navigator, my response was "why would anyone ever want the navigator pinned open?". I'd like to see it close automatically.
I agree, the navigator panel is even closed when you just open a new tab in the same browser session.
Regarding the justification for this request, we also very frequently have to navigate between different contexts, and even within the same context between folders, tasks ...
In addition wide screen format are common these days, so you can very easily afford to use 10 to 20 % of the left screen side dedicated to the navigator.