Lack when sending SW_HIDE message to window in FS

HiFrom a fsmodule (dll loaded into FS9), i have created a standard dialog (window/form).I set the parent by ::SetParent(mywindowhwnd, fshwnd); (std win 32 API). Now, if i send a SW_HIDE hide message, ShowWindow(mywindowhwnd, SW_HIDE);fs lacks, by 2-3 seconds, until the window is hidden.What can i do to prevent this lack? Anyone else experienced that?Thanks for your help.Regards,Rasmus St