The incredible spinning avatar.

For the most part, I have the hang of Poser now, but one problem recurs. If I'm making a looped animation, and if I've had my avi spin her hips, she'll want to unspin rather wildly at the end of the animation -- just before it loops.

E.g., if I've had her spin around a few times to the right, the avi will feel a big need to spin to the left just before she loops -- even 340 degrees or so. (She won't take the easy way out and just spin that last 20 degrees to the right.) The only way I seem to be able to override this urge is to keyframe each and every frame leading up to the final frame. That works, but it's tedious. Breaking spline doesn't seem to work. Is there any other way to convince the avi that she need only turn 20 degrees right instead of 340 to the left?

Because your animation is overrided by the SL default animation.
See what Archanox Underthorn said.

That's very helpful info; I didn't know about that. As it happens, I pretty routinely adjust every joint on frame 2 anyway.

But my question is about behavior inside Poser, not inside SL. In Poser, if I twist the hips say 300 degrees right (spinning my avi like a mannequin), when it comes to loop back to my starting position, Poser interpolates not by spinning me right another 60 degrees, but by spinning me left 300 degrees. Breaking spline does not seem to fix this. The workaround is to keyframe every frame of that final spin, but ugh, what a pain. Any better workaround?

Inside Poser?

Your figure must be set the defalut position on the first frame, which means the hip's rotation is 0 degree. If you would involve the first frame in the loop you said, it was so natural not to be able to loop correctly that you should have never said such a thing, I hope. Whenever you make sure the loop, open the Animation Pallete and tweak Play Range on the bottom of the screen so that it should be set from the 2nd frame to the last because SL animation would be actually played within that range.
OK, you should never said such a thing... but I couldn't figure out what you said.

I post an animation which I set the 1st frame is default, the hip rotation is -300 degrees on the 2nd frame, it is 300 degrees on the 15th frame, and it is -300 degrees back on the last frame. I can't figure out what the problem is. I want you to show us like this.

Oh, sorry, I wont be able to check this forum for a couple of days.