Tuplet creation changes note-duration of the first note in the tuplet

When creating a tuplet I followed the approach mentioned in the manual: enter the first note of the tuplet and press ctrl-3. This leads to a tuplet being created, but at the same time the duration of the first note is halved. So for example when starting a tuplet of quarter notes, the first note is changed to an eight note by pressing ctrl-3, the other notes entered later are fine.