Shared Symbols/Libraries...

Who here has had luck with shared symbols imported to one movie from a library file? I've had inconsistent luck; sometimes it works great (usually if the shared symbol doesn't move); othertimes they do bizarre things like create blips in the animation, change symbols during runtime but not on the timelines or they just appear as blocks or blobs. I am putting an instance of a shared symbol on the stage of the library file (I learned that one the hard way).

Is there a trick to using them? Are there unwritten rules around their use? I'm at a loss why I have such inconsistent luck with them. I'm using Flash MX but I also had the problem in Flash 4 & 5.

Any guidance would be appeciated!

Thanks!