Our Jenkins installation has been set up to authenticate users against LDAP directory server. Source code has been stored to subversion. When people commit changes to subversion, they automatically end up to People list on Jenkins . Each user has fields "Your name" and "E-mail address" populated . Field "Your name" is populated with user ID / login name. The same user ID is used in svn commits. The "E-mail address" field contains a valid email address.
When a build is triggered manually, the Status page of that build  contains a piece of information: "Started by user XXX". The XXX is a link to user data . Similar links are used on the Changes page of a project .
All is fine if the "Your name" field in the user data is left untouched. Sometimes those user IDs can contain all kind of additional coding, which makes them very cryptic. Therefore, it is very tempting to change them to something more human-readable. Changing "Your name" field from "js1234de" to "John Smith" breaks the link XXX on page . The link points to "..user/John%20Smith". Similar links on page  are not affected. They still point to "..user/js1234de".
There is a similar user name related problem with Email-Ext plugin (