Why web server can't decode the request body

I have a web app in WeChat, use jQuery ajax to request web server, i found a oddly bug, sometimes web server can't decode the ajax request body, use Wireshark to catch the HTTP log, found the reason is that high position swap with low position for every byte, so web server cannot decode it. look the images below:

correct:

4D 6F 62 69 6C 65 54 65 6C 3D 31 32 33 34 35 36 37 38 39 39 34

false:

D4 F6 26 96 C6 56 45 56 C6 D3 13 23 33 43 53 63 73 83 93 93 43

eg. 4D to D4

Is there anybody can tell me why?