MFC: strange behavior of CDC and DrawText with DT_CALCRECT?

Question

In BeginPrinting, I calculate the printing rect like below. I rely on this to count the number of pages.

    CRect rect(30, -50, 200, -60);
    int height = pDC->DrawText(cstr, &rect, DT_EDITCONTROL | DT_WORDBREAK | DT_LEFT | DT_CALCRECT);

Then in OnPrint, I do the same calculation again. However, the height result is different. I don't know what could be wrong with it.