I have noticed the following.
If you change the field “Interval” for a Recurring Sales Invoices, which should be already issued but its not, and make 0 months, without changing the “Next issue date” the servers stops, at least to my installation (Windows 7).
The other think I have noticed is that the date is not changing unless you pick it from the ativeX calendar, If you change it by typing, the date is not change