In 4D 2004.2 an enhancement has been made to listboxes for entry to a cell from a mouse click.

The original behavior is as follows:
When a second click takes place in a cell, if the mouse cursor remains above (over the top of) the cell, the change to entry mode occurs after waiting the time of a double-click.

The new behavior is as follows:
When a second click is done in a cell, if the mouse cursor does not remain above the cell (the mouse is moved elsewhere), the change to entry mode is immediate on Macintosh and occurs after the time of a double-click on Windows.

So by clicking a second time in a listbox, whether or not the mouse remains over the clicked cell, that cell changes to entry mode.