When the user opens a form with a grid and tries to select all records with either pressing CTRL+A or going to File > Edit > Select all or selecting the checkbox left to the grid header, they will have a bad time because only the records already loaded are selected then.
Data are not loaded fully when there is a huge amount of data to show. AX loads a few and then particially loads more when scrolling.
So the trick to load and select the entire data is to press
CTRL+SHIFT+END at the same time.
This leads to the following message:
And now all records are being loaded and selected!