openx ad serving issues with custom targeting parameters?

hey everyone, we're really scratching our heads over an OpenX custom targeting problem here. we're trying to leverage its advanced features for a new programmatic campaign, specifically around really granular audience segments.

the core issue is that while basic ad serving works perfectly fine, the custom targeting parameters we're defining within OpenX aren't consistently being passed or interpreted correctly by the invocation codes. this is leading to some pretty frustrating incorrect ad delivery where we expect one ad but get another.

we've set up several custom variables like user_segment, page_type, and content_category and associated them with specific zones. the invocation code on our pages definitely includes these parameters, but it seems like the OpenX ad server backend isn't always matching them to the correct campaigns or creatives. we've double-checked variable names, data types (string vs. integer), and the campaign targeting rules in the OpenX UI multiple times. everything looks correct.

for example, we expect ads targeted to user_segment=premium to show for those users, but sometimes we see default ads or even ads for user_segment=standard. it's like the parameter just gets dropped or misread, or something upstream is misinterpreting it. here's a simplified version of our invocation code snippet, maybe someone can spot something obvious I'm missing:

<script type='text/javascript'>
var ox_vars = {
    'zoneid': 12345,
    'user_segment': 'premium', // This is the one causing trouble
    'page_type': 'article'
};
document.write('<scr' + 'ipt type="text/javascript" src="https://ads.ourdomain.com/www/delivery/ajs.php?' + ox_vars.zoneid + '&user_segment=' + ox_vars.user_segment + '&page_type=' + ox_vars.page_type + '"></scr' + 'ipt>');
</script>

are there any common pitfalls with OpenX custom targeting, especially when constructing the invocation URL parameters? or specific debugging steps beyond checking the UI and the client-side code that could help ensure the OpenX ad server correctly processes these parameters from invocation codes, particularly with more complex programmatic ad serving logic? we're really trying to make sure our programmatic ad serving is as precise as possible.

thanks in advance!