[ic] interchanging data between page and include

[interchange-users@interchange.redhat.com (Tim Böckers)]

hi all,
i'm probably just being thick but at the moment unable to figure the 
following:
if i have a flypage with the code
[fly-list code="data session arg"]
[item-code]
[/fly-list]

that works fine and then change it to
[fly-list code="data session arg"]
[item-code]
[include file="templates/mytemplate"]
[/fly-list]

with mytemplate being something along the lines of
[item-code]<br />
[item-field description]

why do the parameters not arrive/ are the tags left untouched?
or what would be even more interesting, how could i get the template to play 
with the values that the including file has got access to?

any pointers would be greatly appreciated as i am pretty lost on this one.

cheers,
tim