If a caller does a WT_SESSION->timestamp_transaction that has multiple comma separated parts, and one or more of the parts are illegal (for example, they set a durable_timestamp before a prepare call), then some parts of the call may be performed, some will not, and an error will be returned.  The behavior is technically predictable, but you need to know something about the implementation, that is, the order that items are processed.  It seems like checks should be made on all parts before "committing" to perform all.  Otherwise, the caller does not know the state of the world after a failure, or we'll need to document the ordering of processing (yuck).

MongoDB is probably unaffected as of now, as it modifies single timestamps in its calls to this method.