You can find a solution for this problem in the FAQ section [
www.flasheff.com].
Anyway here is the question and the answer:
Q: The Target textfield's position changes while the animation is playing.
A: This malfunction appears when the target texfield is initially created as a Static textfield then converted to dynamic textfield . To avoid this problem, the textfield needs to be set as a dynamic textfield before creating it on the stage.