All siblings of the published node are ordered as part of the publication process according to the actual order on the author instance at the time of publication approval.

Be aware that this does not take into account order at any other point in time, such as time of the published version creation (as this order might be already obsolete by publication of other versions).

The original behavior can be restored by setting /modules/publishing-core/config@orderSiblings=false. For details, Roman is the man

NOTE: Update both 6.2 and 5.7 docs.