Hi hainn84,
I have had the same issue with a module i'm adapting and tried your solution.
It works great, thanks a lot.
In addition i'd say that this code seems to work only if it is placed after the {extends} directive and before the {block name='page_content'} directive, like this
{extends file='page.tpl'} {block name='head_seo_title'}{l s='Page title' mod='yourmodulename'} | {$shop.name}{/block} {block name='page_content'}
Need to be confirmed.
Thanks again