Solved.
As I am using typed group to store all my enemy ships I have to set Unique for loadGraphic in my Enemy class everytime I create a new instance.
Otherwise HF optimizes memory usage and store only one graphic object in vertex buffer and when I try to repaint one particular enemy it overloads the vertex buffer.
The following resolved the issue (one small 'true' at the end):

loadGraphic("assets/images/enemy.png", false, 24, 22, true);