When a collection contains invalid options, cloning it will result in a collection created with default options. As a result, collections with invalid options created by an initial sync or using the copyDatabase command may lose some of their properties like their allocation strategy, or become non-capped collections.
Different members on a replica set might become out of sync when capped collections become non-capped during initial sync. In this scenario, or when the original storage strategy for a cloned collection is modified, storage utilization may be adversely affected. Only collections created with invalid options are affected by this issue.
MongoDB production releases 2.6.0 and 2.6.1 are affected by this issue.
The fix is included in the 2.6.2 production release.
Collections with invalid options are no longer cloned.