The version you install doesn't matter, the decision on what to boot happens before any of the rockbox code runs. I believe the only thing that influences what gets patched is the version of rbutil you used. Just checking the release notes now:
1.2.12 (bugfix release) - released 2012-02-06
(all) Boot Rockbox on USB insert rather then the Sandisk firmware on ClipV2, FuzeV2, Clip+, and Clip Zip.
Are you running a version from before then?
By the way, while this is not the source of your problem, you should probably update from 3.13 to the current build. Besides being quite a few years old at this point, things like USB and power management are barely functional on the clip+ in that build.