[Exim] Bug in prefix generic director option?

I have searched the archives for similar issues but found none. Please
excuse me if this is an issues that has already been addressed.

In the interest of maintaining accessibility while minimizing spam I often
use date driven Email aliases in mailto: tags. For example, this being June
of 2003, my Email address on my resume web page is Jun2003@???
(dynamically generated by SSI code). This requires scripting that updates
my alias file once a month.

I am trying to implement a more elegant solution via Exim prefixes. Here is
my director; note that macros are used for domain lookup files...

# Experimental date-driven prefixes
dateprefix_director:
driver = smartuser
domains = "lsearch;VIRTUAL_DOMAINS_FILE:lsearch;REAL_DOMAINS_FILE"
prefix = ${lc:${extract{3}{ }{$tod_full}}${extract{4}{ }{$tod_full}}}-
new_address = ${local_part}@${domain}

Running "exim -d9 -bt jun2003-username@???" yeilds
"dateprefix_director director skipped: prefix mismatch". Using print_debug
I have verified that the prefix definition equates to "jun2003-", so the
problem is not with the prefix definition. I have also tried using a macro
for the prefix definition with similar results.

If I replace the generated prefix definition with a hard definition, then
the prefix matches, as such...

#prefix = ${lc:${extract{3}{ }{$tod_full}}${extract{4}{ }{$tod_full}}}-
prefix = jun2003-

It appears that the prefix definition is not being subjected to string
expansion. I don't know if this qualifies as a bug report or a feature
request, but I do think that it would be consistent to expand prefix/suffix
definitions.

Anyone else agree or disagree? Is there a good reason why prefix/suffix
definitions should not be expanded?

Thanks. - John R. S.