When trying to manually change the sort order of any collection I get the following error message:
Database "/Users/Dan Donovan/Pictures/Lightroom/Lightroom 5 Catalog.lrcat": AgLibraryCollectionImageOzSortOrder.positionInCollection may not be NULL
Statement: INSERT OR REPLACE INTO AgLibraryCollectionImageOzSortOrder
( collectionImage, collection, positionInCollection, ozSortOrder )
VALUES( ?, ?, ?, ? )
Some others have reported this on the official feedback forum:
Please add your opinion and votes to those threads. The threads include some workarounds you might try.