UPDATES ON THESE BUGS: (I would update the original post but I can't), here's the solutions for posterity, in case anyone has the same issues:

SOLVED - If there is any scaling of a body part, the body part welding breaks down and shows a significant crack in the rendered figure joint. UPDATE: this was a major dealbreaker for me but is now solved; turns out if you go Figure > Skinning method and switch it to Unimesh, it's all fine. Superfly changed the way it handles welding after Poser 11, so this update needs to be selected or things break.

SOLVED - Poser asks my Mac if it can screen and audio -capture my Mac every few hours (because I was denying permission). UPDATE: it turns out that's a color picker thing and Poser has been less buggy / crashy since I've enabled that option. I was suspicious of it but after googling, found lots of references to things like Adobe Illustrator having the same issue - it's Mac's paranoid system settings getting in the way rather than Machiavelli Poser reporting back - though it could still be that, but let's hope not.

SOLVED - If I click-drag to pan the camera using the Camera Controls, the 'selected' item under Parameter Dials snaps to the camera dials, rather than remaining on the figure. UPDATE: this no longer happens, which is great. It was probably the screen capture thing above causing the bug.

SOLVED - When I select a figure/body in a scene and hit the delete button, sometimes the Library window itself goes blank white, and Poser throws up a constant bug error. UPDATE: this still happens, but you can right-click in the window and select 'Forward'. Restarting Poser also clears it, it's apparently just a Safari browser issue (it's all about delete being 'back' and if there's no back to go to, Safari [which is presenting the Library window] now shows a blank nav pane, hence 'Forward' solving it).

- If a figure uses hair strands / follicle surfaces, the whole thing has a delay of up to a second whenever moving the figure, making it very difficult to work with in a scene. UPDATE: according to Poser support, I could reduce the verts etc to solve this. I reduced all the hair display settings so much the figures had very noticeably patchy, jagged hair, and it still displayed with the same delays ... but I think this may be a problem of my chosen working display mode (I use Hidden line Wireframe all the time), so I'll probably just have to live with it, though I don't understand why older versions of Poser were fine displaying hair and #13 isn't, it's probably just changes in the way Poser presents previews rather than an actual bug.

Outstanding issues - (1) Area render does not render the area you select. (2) When conforming one figure to another, Poser likely to crash. (3) Queue Manager takes over 100 x longer than a direct render. (4) Working with custom morphs much more likely to crash Poser than ever before. UPDATE: these are still issues, but I haven't yet raised support tickets for them. Probably only the Queue Manager issue is one I'd like to solve; I'll comment on this thread if I find a workaround.