Multivalue fields in Domino documents that only contain a single value are not returned as arrays while multivalue fields with multiple values are. This inconsistency means you need to convert it into an array if you want to use it in a repeat control. The same occurs with @DBLookup and @DBColumn.
It would be nice to see something like this function be added to the @Function Extensions : http://dontpanic82.blogspot.com/2010/09/xpages-helper-function-for-inconsistent.html but give at a name like @makeArray