Look at https://bugs.debian.org/1074789
message #15 was sent before message #10 but arrived later due to
greylisting, and the interface shows the emails in order of receipt
apparently, This makes reading the bugmail rather harder than it has
to be.

Control: reassign -1 debbugs
Control: forcemerge 336971 -1

That the mailbox is ordered this way is a consequence of the design.
#336971 is the request to add support by ordering by Date or additional
threading options.