Form flickering after a minimize happened in mdi parent form

Question

I used the code here

https://stackoverflow.com/a/3718648/2006502

to prevent flickering of form(MDI form). And the code (to turning on WS_EX_COMPOSITED style flag written in my MDI parent form) also affect all child form in which the above is MDI Parent. That is no flickering on any form load. The problem is when i minimize the MDI Form and then maximise, the all child forms started flickering on load. Can any one have an idea?