STR: 1. Tap in address bar. 2. Enter a search query. 3. Tap one of the quick-search engine icons. 4. The quick-search engine's result page will load with your search query. 5. Tap in the address bar again. RESULT: The address bar retains your original search query, not the quick-search result page's URL. I had quick-searched for something on Wikipedia. I wanted to copy/paste the Wikipedia URL to another app, but the address bar had my original search query instead of the Wikipedia page's URL.
This is actually the expected behavior; see bug 1189870. If you want to copy the URL, you can long-press the URL bar and choose Copy Address.