by Adam Barbary.
I was under the impression that the + designated a nightly build, so you will need to include the build number.
eg. I have in testing Moodle 2.9.3+ (Build: 20151119), but the latest is Moodle 2.9.3+ (Build: 20151209)Version 2015051103.06Stable version.
I cannot reproduce your error in my environment.