<p>So I can see that visiting "<a href="http://www.openstreetmap.org/search?query=%s">http://www.openstreetmap.org/search?query=%s</a>" does error in the way you describe, but I can't get my browser (Firefox 42 on linux) to actually do that. My bookmark looks like:</p>

<p><a href="https://cloud.githubusercontent.com/assets/147741/11621522/d4a9747a-9cb4-11e5-8557-feca0a6bbb46.png" target="_blank"><img src="https://cloud.githubusercontent.com/assets/147741/11621522/d4a9747a-9cb4-11e5-8557-feca0a6bbb46.png" alt="screenshot from 2015-12-07 07-31-44" style="max-width:100%;"></a></p>

<p>and typing "os" in the URL bar replaces the %s with the empty string.</p>

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