When you change a vsites existing speed limit in the GUI and click apply the change is saved to the config files but is not applied to the running apache process. This seems to be a known bug in the cband module itself.
See : http://sourceforge.net/tracker/index.php?func=detail&aid=1495526&group_id=154335&atid=791368
However its been open for a while and has not been assigned to anyone.
The root cause is that Sausalito sends apache a graceful restart signal after the change is saved and mod_cband doesn't reload the config files at this point so the old limits still apply.
To make the change take effect on the running apache Sausalito needs to do a full restart instead of a graceful one.