You're welcome, but changing to the 64bit version might not be the real fix to the problem.
I have a feeling that installing the 64bit version might default the PDF to 1.3, which could make it look like the problem has been fixed but it really hasn't. All that could have happened is that the PDF version has been changed from 1.4 to 1.3, which works, but isn't a real fix.
I have the 64bit version and I got the same problem as you when I exported to PDF 1.4.
I didn't have the same problem when I exported to PDF 1.3.
If you can get on with what you need to do then that's fine, I'm just saying that there could be a more basic underlying issue that may need to be addressed, but I'm not the right person to address it.
Maybe someone who really knows about PDF fields can look into this more extensively.