Bug.search doesn't seem to return a "Flags" field for results as is specified in http://www.bugzilla.org/docs/tip/en/html/api/Bugzilla/WebService/Bug.html I haven't yet tried with Bug.get itself, but docs suggest the format should be the same.
That is the upstream documentation. Red Hat Bugzilla does support it. However, the flags value must be specified in the include_fields or extra_fields argument. See https://bugzilla.redhat.com/docs/en/html/api/Bugzilla/WebService/Bug.html#get for more details. -- simon