I use

thisform.mygrid.recordsource='myselect'
thisform.mygrid.init()

I know, you aren't supposed to fire the init method again. At least, that's what some people have told me. But in my scenario, it was the only solution I could find, especially if you are changing the structure of your recordsource.

You may try refresh() instead and see if it works for you.

Hope it helps, steve