Description:
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I've tested the code on multiple versions of PHP, no matter where I test I get the same strange behaviour, actually really curious as to how this is even possible.

It evaluates 'n/a' == 0

Even though they are obviously not the same thing.

In the demo script the bug happens on the second option where I check whether the posted value is the same as the field value and if true I output 'selected'

What you would expect to happen on load is that only the default value would be selected, however for some strange reason both 0 and n/a == n/a

This code has been tested on at least 3 different machines, including on my own server here at https://www.differentiality.co.za, where I'm running the latest released version of PHP straight from apt-get.

Please do contact me if I can be of any more assistance.

Test script:
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I've posted a link to the page where the bug can be reproduced at PhpFiddle
http://phpfiddle.org/main/code/4sr3-cq2w

Expected result:
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<option data-comparevalue="n/a" data-value="n/a" selected value="n/a">Please Select</option>
<option data-comparevalue="0" data-value="n/a" value="0">Please Select</option>

Actual result:
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<option data-comparevalue="n/a" data-value="n/a" selected value="n/a">Please Select</option>
<option data-comparevalue="0" data-value="n/a" selected value="0">Please Select</option>