Cannot scroll in datagrid smoothly

[Grey]

I have one button and one datagrid in the winform. First, I highlight anyone
row in the datagrid and scroll. However, when the highlighted row scroll to
upward, the focus was set back to the button automatically which would cause
the datagrid cannot be scrolled anymore. I need to highlight the datagrid
again if i need to continue the scrolling. How come of this happen and how
to solve it??

Million thanks