I have seen this phenomenon several times since I switched to DDG but today it's really bad.
I searched for "gold price" in iOS 7 Safari and got only one ad link back, nothing else. If i followed up with "gold", same problem. However if I close the tab and start DDG in a new tab, I get results for "gold" alone, but once I try to search for "gold price" again, I would get just one ad link again. Same for "silver price". I disabled Instant Answers but got the same problem.
In the past this happened on a couple other searches, including at least one in IE 10 on Windows 7. I thought it was an IE bug but now it's bugging me. Obviously a search engine should return results!
Could someone try this out? DDG: feel free to contact me and I can send you a video of the issue.
Update: added screen capture .
More update: I just tried "gold price" 20+ times on a friend's Nokia Windows Phone and it did not have the above problem. So I guess it's a browser support issue?? Bad scripting?