Please attach the .xtc here in the forum, or reply to the email I sent you directly with them.
Now we are homing in on Notes and Windows, involving bad loading and saving, we are getting somewhere because there are BOTH platform specific code parts AND the format of the Notes entries has changed a lot between versions.
The old code at parm <12 and >9 was a single line of setup, several lines of content and a terminating END
the new format is just one line
The text string(s) (for Windows is also UTF8 encoded rather than system codepage).
The new code should read in the old parmlevels of .xtc correctly, however. I suspect that the issue is somewhere in all this.
By reading in a V5.1.2a NOTE badly it is likely mangling some definition following it (hence your missing stuff) and then writing the badly read note out in the new V5.2 format causes some exception (there is an assert if the type of the Note object is not >0 and <2, for example). There even seems to be an issue with writing a simple note at V5.2 level on Windows based on other's observations as well.
The input .xtc will show us a lot, I expect.