Pop-up lists sporadically refuse to drop-down!

Background:

I created a stand-alone kiosk application using FM_dev5.5 consisting of multiple files, multiple relationships and multiple value lists. Some of the value lists take their data form a related field.

Problem:

The application works fine, pop-up lists work as they should, until sporadically the following happens: all fields with field format set to 'pop-up list' refuse to show the pop-up list. The field is still selectable, and data can be typed in. Note that *all* fields with pop-up list show this behavior: changing to another layout, selecting another field with another pop-up list, results in the error that the pop-up list does not drop-down. Selecting the field and pressing the 'ESC' key will let de pop-up list drop-down, but no item can be selected. Quitting and restarting the kiosk application resolves the behaviour of the pop-up lists.

Other debug info:

Pop-up menus do not suffer from this sporadic 'bug'. Making a copy of the field on the layout and setting one copy to field-format 'pop-up list' and the other to 'pop-up menu' shows that the menu drops down on mouse click, while the pop-up does not.

Hope somebody experienced the same buggy drop-down behavior of pop-up lists and found a solution... would be happy to hear about it!

Regards,

Stefan.