I just found one interesting grid 'feature' and it might be helpful for all struggling with grids. You obviously know that grid used to become blank when its recordsource is overridden. Also, you probably know that one of ways to fight it is to base grid on permanent cursor and refill it using ZAP/APPEND. So far, so good, last hour I found that even this grid can become blank, if ZAP issued when focus is on the grid and new recordsource RECCOUNT() is more than previous recordsource RECCOUNT(). I understand that it sounds crazy, but it's really so, at least for grid I have right now :-).
However, if focus shifted to another control (setfocus) right before ZAP, then grid is Ok, so it's still workable.