1. Block start with different chars::
Linux:
 HEX            ASCII
FF E1 0B 24     .$

Win:
FF E1 0B 25     .%


2. After the slash in "/xap/1.0/ - And before the tag <?xpacket
I have this:

Linux:
  - HEX -    -   ASCII  -
2F  00 3C    -  /.<

Win:
2F  20 00 3C - / .<


When I change 20 to 00 in a hexeditor, i get this:

$ exiv2 -p x fromwin.jpg
XMP Toolkit error 201: XML parsing failure
Warning: Failed to decode XMP metadata.
fromwin.jpg: No XMP data found in the file