However, my only clue on the Preview Mode screen that something is going on is a small indicator at the bottom of the screen that says "Exporting toolpaths..." There's a status bar to the right, but it doesn't give any indication about what's going on or the status of the process.
And, in fact, just taking this screenshot seems to have disrupted it, because now , because now there's no indication about what the program is doing at all. I assume it is still trying to export the toolpaths, because if I try to Save the Toolpaths to Disk again or exit Preview mode now, the program crashes, and I need to start all over again.

It would be nice if the save feature was a little more robust and a little more informative.