Looking at the source for one of your PHP calculators (ie: here), I see that it uses JavaScript for certain functions (ie: "calculators.js"). That's most likely the source of the problem. Pages fetched via Ajax will often "lose" the JavaScript included on the page, as Ajax basically cuts and pastes the fetched content onto the page without reinterpreting the JavaScript on it.
You can try manually adding any external .js and .css files referenced in your PHP calculator pages to the main page containing Ajax Tabs Content script, so they are always available. This may or may not work still, however:
Code:
<link href="calculators.css" type="text/css" rel="stylesheet">
<script type="text/javascript" src="calculators.js"></script>
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