which file attributes are you changing and how?
i am unable to repeat your problem, and i have no idea why explorer would recompress jpgs by changing attribs.
do you mean the info shown along the bottom of the explorer window?
that information does get stored in the actual image file, and is readable by other software.
i've always found that adding data her in explorer adds about 6 kb to the file size, but i've never noticed any recompression going on.
but then i don't have any 8 meg jpgs - i suppose i'll have to make some and test.
*edit* just tried it with a big jpg - no noticable difference in file size. they certainly haven't be reduced to a quarter.
more testing needs to be done...