When inserting documents, MongoDB validates the values for certain fields for correctness. For example, the _id field cannot be an array. A bug in the insertion code caused this validation to stop after the first encountered timestamp field and would therefore allow documents to be inserted that would normally not pass validation.
This can cause invalid documents to be stored in a collection. This in turn can cause problems when the invalid document is later read.
The issue only arises if users attempt to insert documents with invalid values. However, if users want to rely on this safety check, they can place any timestamp fields at the very end of the document to avoid this issue. Note that some drivers may not preserve the order of fields in a document.
MongoDB 2.6.0 and 2.6.1 are affected by the issue.
The fix is included in the 2.6.2 production release.
The problem was an erroneous break statement that would prematurely end validation. The break has been removed.