Weird text frame resizing issue

Hi

I have a text frame -- I resize the text frame vertically so there is plent of room. I paste text into it using:

     ps = sourceFrame.parentStory.texts[0]

    sel = ps.characters.itemByRange(begin,end);

    sel.duplicate(LocationOptions.AFTER,destinationframe.parentStory.inse rtionPoints[-1]);

which works fine. The text appears with a Paragraph symbol at the end, as well as the# end of file marker.

I then resize the frame using

       gb=frame.geometricBounds;

        gb[2]=frame.lines[-1].baseline;

        frame.geometricBounds=gb;

which SOMETIMES resizes the bottom to align with the bottom of the last line of text (as desired) with the # overset.

Sometimes the # appears on the last line by itself, and the frame resizes to below the # (not desired action)

If I then select the frame and run the following:

frame=app.selection[0];

        gb=frame.geometricBounds;

        gb[2]=frame.lines[-1].baseline;

        frame.geometricBounds=gb;

it resizes properly.

Any idea WHY?

TIA