The ls command seems to be slightly broken in the wu-ftpd included RH 7. The plain "ls" command returns only the list of files - directories are not included as with a console "ls" command. Adding options to the ls command, such as "ls -l" appears to cause it to behave correctly. This behavior is changed from previous versions, in which the "ls" command behaved exactly as it does at the console. The workaround above is fine for interactive use, however, this bug is breaking automated clients such as the perl "mirror" package.
After checking various websites, I found that this is apparently intended behavior by wu-ftd. I also found a patch for the mirror client on the mirror website. Still, this is surprising and non-traditional behavior, and might merit a FAQ or other note.