some parameterized logging messages in ZK are using a wrong parameter syntax making the logging output pointless in some cases
e.g.
https://github.com/zkoss/zk/blob/master/zkbind/src/org/zkoss/bind/impl/BinderImpl.java#L354

_log.debug("doPropertyChange:base=[%s],prop=[%s]",base,prop);

the SLF4j docs explain that '{}' are used for parameterized messages instead of '%s'
http://www.slf4j.org/apidocs/org/slf4j/Logger.html

Likely other classes are affected too after the change to slf4j.