Wicket example "Library" - sign out not working

Steps to reproduce :
1-Click on the "library" example
2-sign in
3-sign out

Step 3 produces :
HTTP ERROR 500

Problem accessing /library/wicket/bookmarkable/org.apache.wicket.examples.library.SignOut. Reason:

Header was already written to response!

Caused by:

java.lang.IllegalStateException: Header was already written to response!
at org.apache.wicket.protocol.http.HeaderBufferingWebResponse.checkHeader(HeaderBufferingWebResponse.java:62)
at org.apache.wicket.protocol.http.HeaderBufferingWebResponse.addCookie(HeaderBufferingWebResponse.java:69)
at org.apache.wicket.util.cookies.CookieUtils.save(CookieUtils.java:297)
at org.apache.wicket.util.cookies.CookieUtils.remove(CookieUtils.java:233)
at org.apache.wicket.util.cookies.CookieUtils.remove(CookieUtils.java:80)
at org.apache.wicket.authentication.strategy.DefaultAuthenticationStrategy.remove(DefaultAuthenticationStrategy.java:151)