The automatic encoding can actually get you into trouble -- because you need to HTML encode the ampersands as & -- so, either of these two would be valid:

<input type='hidden' value='search&amp;l=phone&amp;s=$query&amp;r=100&
+amp;m=&amp;p=$cnt'>
<a href='$url?search%26l%3dphone%26s%3d%24query%26r%3d100%26m%3d%26p%3
+d%24cnt'>
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And once you realize that, it makes perfect sense why there's the push to use ; as its seperator (which you don't need to HTML escape)