xsl param fails in PHP 5.3x

Question

I have an in PHP 5.3 that is failing when something is its contents.

For context I do a XSL transformation on one DOMDocument and insert the results as a parameter into another DOMDocument that is then transformed. This has worked fine until now.

<h5>lets see: <xsl:value-of select="string-length($content)" /></h5>

returns 0.

$content

is the param name.

In my PHP I can get this to work a thousand time elsewhere but for some reason on this occasion it only fails on inserting circa one thousand names into an HTML table. If I swap the names for something else e.g. the autoincrement ID then it works fine.

I have no double/single quote issues, as everything is run through a cleanup utility and I have manually gone through the data and removed everything but alpha numeric characters.

Is there a max lenght/size with xsl param's? Otherwise.......help????