This was unexpected, I would assume that a UFO export doesn’t mess with something like that. What else is the UFO export changing?
That’s a difference between export and save.
Would you care to elaborate what the differences are since the handbook does not list the differences.
Not sure I understand the question. An export can be expected to be fundamentally different from the source file. That is true for any app.
In an export, combining marks are set to zero width, like they are in an OTF export.
I just tried and it didn’t change the spacing. Did you check the “decompose smart stuff”? Setting the combining marks to zero width is part of that “stuff”. Without that checkbox, it should keep the width.