i placed this in top right cell (width=210 and height=252) of my Grid.
and if the text to be displayed in textblock contains much text to be scrolled down to read,
the complete page of my App, flickers.
if the text is just enough to be read without scrolling down,
the flickering is not there.
also, i used the same code on other page with increased width and height,
the scrolling is very smooth.