invalid delivery-id sent or out of order delivery when credit is close to or greater than session window

E.g. the following trace is from the client side (the peer was qpidd) and appears to show a delivery-id being skipped:

[0xb2a800:1] <- TRANSFER @20 [1, 1520, b"\xf0\x05\x00\x00\x00\x00\x00\x00", 0, false, false] (177) "\x00Sp\xc0\x08\x05BP\x00@@R\x01\x00Ss\xd0\x00\x00\x00\x11\x00\x00\x00\x0d@@@@@@@@@@@@@\x00St\xd1\x00\x00\x00\x1a\x00\x00\x00\x04\xa1\x02snp\x00\x00\x16\xbd\xa1\x02ts\x80\x12\xc8\xfb\xe4\xdb\xd1\xc5\xdf\x00Su\xa0dXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
[0xb2a800:1] <- TRANSFER @20 [1, 1521, b"\xf1\x05\x00\x00\x00\x00\x00\x00", 0, false, false] (177) "\x00Sp\xc0\x08\x05BP\x00@@R\x01\x00Ss\xd0\x00\x00\x00\x11\x00\x00\x00\x0d@@@@@@@@@@@@@\x00St\xd1\x00\x00\x00\x1a\x00\x00\x00\x04\xa1\x02snp\x00\x00\x16\xbe\xa1\x02ts\x80\x12\xc8\xfb\xe4\xdb\xd1\xe8c\x00Su\xa0dXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
[0xb2a800:1] <- TRANSFER @20 [1, 1522, b"\xf2\x05\x00\x00\x00\x00\x00\x00", 0, false, false] (177) "\x00Sp\xc0\x08\x05BP\x00@@R\x01\x00Ss\xd0\x00\x00\x00\x11\x00\x00\x00\x0d@@@@@@@@@@@@@\x00St\xd1\x00\x00\x00\x1a\x00\x00\x00\x04\xa1\x02snp\x00\x00\x16\xbf\xa1\x02ts\x80\x12\xc8\xfb\xe4\xdb\xd2\x8b\x95\x00Su\xa0dXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
[0xb2a800:1] <- TRANSFER @20 [1, 1523, b"\xf3\x05\x00\x00\x00\x00\x00\x00", 0, false, false] (177) "\x00Sp\xc0\x08\x05BP\x00@@R\x01\x00Ss\xd0\x00\x00\x00\x11\x00\x00\x00\x0d@@@@@@@@@@@@@\x00St\xd1\x00\x00\x00\x1a\x00\x00\x00\x04\xa1\x02snp\x00\x00\x16\xc0\xa1\x02ts\x80\x12\xc8\xfb\xe4\xdb\xd2\xa8\xa5\x00Su\xa0dXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
[0xb2a800:1] <- TRANSFER @20 [1, 1525, b"\xf4\x05\x00\x00\x00\x00\x00\x00", 0, false, false] (177) "\x00Sp\xc0\x08\x05BP\x00@@R\x01\x00Ss\xd0\x00\x00\x00\x11\x00\x00\x00\x0d@@@@@@@@@@@@@\x00St\xd1\x00\x00\x00\x1a\x00\x00\x00\x04\xa1\x02snp\x00\x00\x16\xc1\xa1\x02ts\x80\x12\xc8\xfb\xe4\xdb\xd2\xc01\x00Su\xa0dXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
[0xb2a800:0] -> CLOSE @24 [@29 [:"amqp:session:invalid-field"]]
ERROR amqp:session:invalid-field sequencing error, expected delivery-id 1524, got 1525

It is of course possible that I am doing something wrong in the broker code, but I can't think what would cause something like this (since I can't influence the delivery ids directly). It only seems to happen when there is a prefetch greater than 900.