[Building Sakai] User properties missing

[Joshua Swink]

I have some code that's processing users in Sakai, and at one point
it's looking for some property or another:

user = getUserDirectoryService().getUserByEid(studentEid);
[...]
String propVal = user.getProperties().getProperty(propertyName)

The result is null. The problem is that I know this property exists -
I can look in the database and there it is in SAKAI_USER_PROPERTY. It
has been there for several weeks, and Sakai has been restarted since
then. For 99.9% of the students processed this way, all properties are
found. But there are a few where this property (and some others) are
missing. They tend to reappear after a while.

Any idea what's causing this? I am using Sakai 2.6.1 with Oracle.

Josh