Mmh ...

On my Vue 7 Infinite i CAN reproduce, what you've just mentioned - meaning, i load the sample scene "Autumn" - render it, and selecting "save picture" nothing happens, i CAN'T save it either ...
And - loading sample scene "Ecolo-Go" i CAN save it without a problem.

But then, what i did made it working for me:
I've loaded sample scene "Autumn" again - rendered it in "Full" quality - tried to save it - not working again, like the first time and like you've described.
Then i just saved this sample scene with a new name like "Autumn1" - rendered it - and selecting "save picture" finally the save browser appears and i CAN save the render.

Weird .... and you can't reproduce, what i'm doing with your Vue version ??
Wondering ... strange, that i have similar problems like you, but i can get rid of them with a simple scenery save ...