Scroll problem:child window

Hi
I have and dialog and child window in it.
In this child window i have button as a child window.

When user scrool in dialog. I get a message and try to scroll child window by ScrollWindow. All works button moves. But when i stop scrolling,button return to it's start place(i.e when i scrolling button go to the edge of window,but when i up mouse button,button returns to its start place).Why?

Code:

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CDialog:
childWindow.Create(NULL,NULL,WS_HSCROLL|WS_CHILD|WS_VISIBLE,Rect,this,0);
SCROLLINFO scrollInfo;
memset((void*)&scrollInfo,0,sizeof(scrollInfo));
scrollInfo.cbSize = sizeof(scrollInfo);
scrollInfo.fMask = SIF_ALL;
if(GetScrollInfo(SB_HORZ ,&scrollInfo,SIF_ALL))
{
childWindow.SetScrollInfo(SB_HORZ,&scrollInfo,TRUE);
childWindow.ShowScrollBar(SB_HORZ,FALSE);//use not own scrollbar
}
void OnScrool(WPARAM wParam,LPARAM lParam)
{
int step = 100;
childWindow.SetScrollPos(SB_HORZ,pos,TRUE);
childWindow.ScrollWindow(-step,0,NULL,NULL);
childWindow.UpdateWindow();
}
CChildWindow:
CButton btn;
btn.Create("OK",WS_CHILD|WS_VISIBLE,CRect(0,0,100,20),this,0);

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