why is my animation doing its own thing?

I'm testing an animation on the beta grid and i keep finding that no matter what i do for some reason the animation 'drifts' and jerks back when it loops.

i thought it was me, so I've made the looped bit identical frames with a 1 second ease in and out (although why it should matter if there's no movement at all escapes me, but i thought I'd try it)

and the animation drifts.. logically it shouldn't as it's not moving at all for around 5 seconds before the loop and then during the loop.

I'm assuming this is a bug. I've spent hours tweaking absolutely everything until i ended up with this static pose and it still does it..

is there a jira? is there anything i can do? (apart from pull my hair out of course)

My first feeling would be to wonder if the difference in your frame before the end is enough so the optimization isn't taking it out? (So in effect looping from the position at the 2nd to last, instead of the frame you copied from frame 2 to the end maybe?)

If not, yes, there has been this jira, and now I see it's been issued a LL id too:

nope.. found the jira..

http://jira.secondlife.com/browse/VWR-2387

adjusting the final frame to compensate for the drift does work, but it's painstaking as it's all guesswork as to how much each part has drifted..

there is a marked difference between frame 2 and where the loop begins. this one is definitely another quality LL 'undocumented feature' and it's only been broken since 2006 lol