Thanks for pointing me to the JIRA issue Thomas.
About templatexe standard wiki issue: yes this is
known and fixed, it
will be part of XEM 2.1.2. See
http://jira.xwiki.org/jira/browse/XAWM-110
Note that this wiki is not absolutely needed, you can
create a empty
virtual wiki (without any template) and import the xar you want for it
like you would do for any XE installation. The template is just an
help when you want to create a wiki which is a XE of the same version
as XEM bout you could want to create something else like Workspaces
instead of XE.