Version:            (using KDE 4.1.2)
Compiler:          gcc-4.2.3 
OS:                Linux
Installed from:    Gentoo Packages

When I create a (weekly) recurring To-Do and set a due date only (but no due time), and then later tick the checkbox to mark the To-Do as completed, no new entry for the next week is created automatically. The To-Do just remains in the list, with its status being "completed". 
If I do specify a due time, it works as expected: upon marking as completed, the current To-Do is removed from view and a new, not-completed To-Do is created with a due date/time in the future according to the recurrence settings.