Fraction Bars in MathType and Word Equations

When I upgraded from Word 2003 to Word 2013, I noticed that the thickness of fraction bars (and perhaps some other horizontal lines) in MathType equations varies with document zoom. Sometimes the thicknesses are different in nearly identical equations, and even within the same equation. In many cases, the lines are so thick that the resulting document is essentially unusable. I seldom see a problem at 100% zoom, but it sometimes happens at greater zoom values. For a given document, the zoom value at which the problem appears is consistent, but the value seems to vary among different documents with different equations. The problem will usually appear if I try zooms of 125%, 150%, and 200%, but sometimes it’s easier to find by changing zoom with the mouse scrolling wheel.

I can find slight variations in line thickness in PDFs generated with Word 2003 and earlier, using Acrobat versions from 4.0 to XI, but nothing like what results with Word 2013 and Acrobat XI or Acrobat DC (2015). So as with equation links, there seems to be a strong correlation between this problem and the change from Acrobat Distiller to Adobe PDF Library.

I get the same problem using Word’s native equation generator, though in the few examples I’ve tested, the thickness variation isn’t as great as that with MathType equations. Nonetheless, the result is nearly unusable for any purpose in which the author wants to be taken seriously.

I do not see the problem using groff and creating a PDF from the Postscript file using any version of Distiller, including 15.0. I also see no problem in a PDF generated from Texinfo source using MikTeX pdfTeX-1.40.15.

Anyone else notice this?

Any suggestions, especially from Adobe, WIRIS, or Microsoft?