Dropdown select list is (erroneously) empty

[Filip Callewaert]

Erroneous behaviour I've seen lately several times: adding an entry to a dbase, and willing to select a value in a dropdown list (linked to another dbase) gives me no options to select from. 

This happens after having selected a value for one entry, but for the next entry it does not work any more, only an empty list is shown. 

The screenshot:
I added an entry, selected the value "Colruyt" for field1. Field1 is linked to another database.
I add another entry, want to select the value "Colruyt" again, but my dropdownlist does not show any values at all. 

Saving changes does not help.
Only refreshing the page provides me again with the select-list.