Right -- for a moment I worried that we were missing out on some input sanitization but that's not the case. Not only Bobby Tables, but Bobby Backticks and friends all register ok. Only bobby Smiley fails, because ':' is the filed separator in /etc/passwd and there is no escape sequence for it.
This gets cured with http://dev.laptop.org/git/projects/idmgr/commit/?id=2384a1b0b578c3fc9eeaa5e8b7d9c1617ca9f0eb which just removes it.
Which is rolled in a nice idmgr rpm for the 0.6 series.
yum --enablerepo=olpcxs-testing install idmgr
should bring idmgr-0.7.22 (or newer).