So what does it do?
There's an identified and reported bug in export when "Don't Enlarge" is checked, and it results (in certain defined circumstances) in any "Resize" options being ignored and the file is exported with original dimensions. Is that what is happeneing in your case? Is unchecking "Don't Enlarge" a viable workaround until the problem is fixed (hopefully in the next release).
It fails to shorten to the maximum long edge requested, leaving longer-edged files in the exported folder.
Never had this problem with Lightroom4. Just upgraded to 5. My operating system is Windows Pro 8.
Thank you for your time.
Gary Lloyd McCullough
(904) 687-9690 text and voice
As Jim said, there is a bug if you have Don't Enlarge set in the Export sizing options Do you? In other words, uncheck the Don't Enlarge, and then does resize as expected other than enlarging if the image was smaller because you had to turn that option off?