set struts.devMode to true in struts.xml does not effect as the docsays?

[lightning]

I'm using struts2.0.11.1.
The doc says I can put

<constant name="struts.devMode" value="true" />

into struts.xml to enable dev mode,which can reload struts.xml and
everything else to faster out development.

I did it and restart my tomcat, but in fact only more infos are shown
when error occurs, the struts.xml never reload, even my ActionClass
does not reload, it reloads in struts1, version 2 is worse then
version 1????

What did I miss?