There is something wrong with IK armature springs when used in runtime mode. Child nodes become disjointed with user interaction of parent nodes.
Drag spring on right from different points to see bug here: http://gardenofpossibilities.org/flash/ik_spring_runtime_bug/spring_runtimebug.html
I filed this as a bug, but wanted to mention it here in case others have a similar problem or anyone has a workaround:
Steps to reproduce bug:
1. Build simple movieclip based armature
2. add springs to bones
3. set armature to runtime and publish
Armature child nodes become disjointed with user interaction of parent nodes. Same disjointed behavior occurs when armature is moved with actionscript 3 ik.mover.
Armature nodes should remain properly connected when user or actionscript 3 ik_mover moves any node.
When springs are 0 (no spring) armature works correctly. It appears that the problem is caused by child nodes pivoting at parent node head, when they should actually pivot at parent node tail. Also, when armature becomes disjointed, dragging or moving tail node (furthest from root) restores joints.
I posted this two months ago. Does anybody have anything to add on this issue? Are there any Adobe programmer/engineers out there? I've even filed a bug report, but have not received any feedback. Not a peep. Please?
I have no idea what software you are using to create your sample, but it looks like your question may belong in a different Forum. Just a guess, but this doesn't look like a Flex issue.
Incorrect, this is the Flash discussion Forum, not the Flex forum, and the IK Spring example I provided was created with Flash CS5.