I can't produce the run away thread scenario. After an image sequence Poser idles down to less than 0.1% cpu usage. And, the UI remains responsive as normal. However there's a known issue with dynamic hair getting all ... explodey ... and that absolutely does drag the UI down to it's knees. That's a known issue and has proven to be more elusive than expected and only seems to affect Mac. Do your scenes have dynamic hair?

And, the make movie options default behavior is setup to match the P<13 behavior. They were originally defaulted off but then we got crucified because "Poser 13 couldn't make movies" Apparently the Auto Make option needed a flashing light or we needed to default it on.

If you're used to rendering image sequences and encoding in something like Davinci it's annoying. If you're used to Poser doing it it's perfect. Can't please every body.

One huge new benefit is that P13 allows you to encode existing sequences.In most cases it's one click but it can work for any properly numbered image sequence.

1) Click the [Change] button

2) choose the first file in the sequence and remove the underscore and frame numbers (filename.png)

3) OK

4} Poser will warn that you might be overwriting images (That's new in 13 too)

5) Click [Encode Existing Images]

Done

And if you're still in the scene that you just rendered the sequence just click the encode button and you're rescued. Literally one click to get back in your groove.

Once you change the setting they are saved with the scene.