Further investigation shows that the duplicate page 229 has been a P_LEAF page with freelist entries before:
0e5000 e5 00 00 00 00 00 02 00 44 00 14 0c 14 0c dc 0f ... 0e5fd0 e1 03 00 00 38 01 00 00 ab 00 00 00 18 00 00 00 0e5fe0 00 00 04 00 fd f8 a2 07 05 00 00 00 cf 05 00 00 0e5ff0 b0 05 00 00 8b 03 00 00 81 03 00 00 eb 00 00 00
The entry starting at 0e5fdc with data length 0x18 and key length 0x04 looks very much like a freelist entry with transaction number 0x07a2f8fd = 128121085 (which is just a few transactions before the freelist entries in the mdb_stat output above.