There are definitely two different things going on with "manage flights". One (old?) is at:
https://book.jetblue.com/B6.myb/bookingDetails.html
The other is at:
https://book.jetblue.com/B6/ReservationSearch.do
It seems like only one works depending on which particular server you happen to hit.

Also of note is that the itinerary viewed through the latter link is missing the link to the receipt. Luckily you can get the receipts this way:
https://jetbluereceipt.sabre.com/new/m/mEticket.html?action=printEticket&pnr=ABCXYZ&ticke tNumber=2790000000000&eticketTotal=1&pcc=NIH&hostI D=B6