Hi,
If you could please provide some example file showing the problems, I'll see if I can nail them down.
the problem with delimiter autosizing seems to be caused by MPenvironment; however, the problem with subscripts still seems very strange to me (since superscripts work as expected). I've included a test file and the PDF generated by my TeX installation.
Best regards,
Sebastian
nath_test.tex
Description: TeX document
nath_test.log
Description: Binary datanath_test.pdf
Description: Adobe PDF document