Asterisk version is 1.4.21.1 and distribution is Centos 5 - i386. Case is consistent -- for example:
[SIP/7110xb]
type=extension
extension=7110
context=xb1
label=John
mailbox=7110@xb
extenvoicemail=*67110
is the definition related to the UserEvent shown earlier. Assuming you're matching the "Channel:" value with the [SIP/7110xb], there should be no case difference. Of course, you may mean something different.