First, make sure that the "Schedule only at these shifts" option, located just above the shift preference in the volunteer's profile, is turned on. If that option is not turned on, then the scheduler may schedule the volunteer for shifts that are not one of the volunteer's preferences.

However, if the "Schedule only at these shifts" option is turned on, then VSP will NEVER schedule the volunteer for a shift that is not listed as one of their preferences. In cases where it seems like this has happened, there are three common explanations:

1. The shift preference was removed AFTER the schedule was completed.

2. The volunteer was manually assigned to the shift. In this case, provided the preferences were set correctly when the manual assignment was made, a warning message would have been displayed saying that the volunteer cannot serve at this time. However, sometimes people click through this message without reading it and end up adding the volunteer to the shift anyway.

3. The shift they were scheduled for was a "yearly shift" or "one-time-only shift". By default any volunteer will be scheduled for any yearly or one-time-only shift even if their preferences dictate that they can only be scheduled at their listed times and the shift is not one of their listed times. The setting that controls this behavior is located in the "Scheduler Settings" dialog, accessed by choosing "Scheduler Settings..." from the Schedule menu at the top of any open schedule or schedule skeleton window. By default the "Schedule any volunteer for any non-regular shift (regardless of his or her shift preferences)" option is turned on. However, by clicking on the "Schedule only volunteers for a non-regular shift who have the shift (or '[Any special shift]') explicitly declared as one of their recurring shift preferences" option, you can prevent any volunteers who do not have a non-regular shift listed as one of their preferences from being scheduled for that one-time-only shift.