Another date/time/timestamp related problem:
To force the entry of a date with century, I configured a field's
edit and display mask to 'dd.mm.yyyy'. This basically works, but has
two disadvantages:
(1) the user has to enter dd and mm as two digits. Trying to enter
only one digit, i.e. type "1.4.1955" gives an "invalid input"
exception
(2) once a date is entered (and changes are saved or the field just
lost focus) it is not possible to delete the date. Deleting all
characters gives and "invalid input"

Of those issues, the second is the more significant. Anyone has a
workaround or an idea how to enforce the 4-digit year by other means?

Mirco