"Schedule publication" dialog always proposes a scheduling time in the past

When a document is scheduled for publication, the scheduling time in the dialog seems to be initialized with the document's last modification time. This time will always be in the past. Hence, the dialog always shows an error if the user accepts the default value and immediately clicks "OK". An initial value of, e.g., "now" plus one minute would make more sense.

Steps to reproduce:
1. create a new document
2. choose "Publication actions" --> "Schedule publication"
3. immediately click "OK"

Expected behavior: the document will be scheduled for publication at some sensible default time
Actual behavior: an error dialog is always shown