That's great. I have slightly change the test program, basically added more entries.
The following shows when the popup HAPPENED to show as a short rectangle when input string is "br":
The exactly same input of "br", in most time will produce popup like this:
The problem with the short one is that if the "br" was a mistake, I backspace one to change the search string to "b", a lot more entries now qualifies, but the size of the popup will never change before close and open again.
Here is a example of position/size problem:
This happens more consistent. It invariably repeat itself as long as the current row is close to the center of the screen.
Other problems are harder to repeat. I'll do more experiment to see if I can find a rule.