its sounds like you have both systems (A* and steering) affecting things at once. they should at most affect things alternately, not simultaneously. but it also sounds like you have a more fundamental problem of using two rather incompatible systems. as soon as you use steering to avoid a moving object, your A* solution goes out the window. when you're heuristics kick in and do collision avoidance steering, since you use A* for static collision avoidance, you must immediately select a new location to move to (to steer to), then run A* to that point, adding in the object you're avoiding, since you fundamentally rely on A* to get from A to B. this means no real "steering", just recalculating A* when things are about to go wrong.
I'm using A* to set subgoals for my units, and steering to arrive at the goals. It's the way many rts games do pathfinding, I feel quite confident that they can both be compatible. That's not really the issue though, pretty sure my problem would occur even in a simulation that only used steering with seek and flocking behaviors.
Edit: Just for clarification, the only thing a* is set the destination for the "seek" steering behavior