Связался с автором jamwiki по поводу бага с '_', он спрашивает:
I finally got a chance to try to reproduce this issue, but when I create the login alex_custov on my local machine it seems to work for me with both the current JAMWiki code and the 0.6.3 version. A few questions:
-Just to verify, can users without underscores edit pages?
-Have you made any changes to the /WEB-INF/applicationContext-acegi-security.xml file?
-Are there any other customizations you might have made that would affect editing pages?
И вообще, поучавствуйте: http://jamwiki.org/wiki/en/Bug_Reports (в конце)