• When invoking the mason page, add '?=' to the end of the url: 'http://myserver/mypage.mas?=' - this should tell your browser to make a fresh request each time
• Disable your browser's cache and see what happens
• Try running your query through a plain cgi script - mason doesn't cache unless you tell it to, and it doesn't look like you have, but this step will indicate if the caching is happening at the mason/mod_perl level

UPDATE: Put this line in the init block of your top level autohandler

$r->no_cache(1);

this will ensure your page is not cached by browsers and proxy servers. (this is recipe 3.10 in the mod_perl cookbook)