Sorry, I should have included an example. If %param looks like:

( selected => "foo" )
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and $file = "bar"
I would expect the larger snippet of code to give me something like this:

<input type="hidden" name="selected" value="foo:bar">
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when what I get instead is:

<input type="hidden" name="selected" value="foo">
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If I change the hidden() to a Dumper in order to show the contents of %param in place of the hidden input, the values are infact what I would expect. The reason I included the one liner is to demonstrate the inconsistancy.

Ovid definately pointed out a better way that I hadn't thought of but I am still curious what the goofup is here. To get the full operation of the script means posting a lot of code and it its not something obvious, I'd rather just drop the issue and dtrt.