XF 1.4 Member Search not working at all

One of our members complained today that the "Find Member" search on the members page returns no results. I was surprised to discover that this indeed is broken. When you type in the field, it will pop up the hover box with matching names, but if you click on one of them it does nothing at all (other than clearing your text and returning you to an empty search box).

Any tips on diagnosing this issue? There is nothing in the error log when I do this.

We have the following addons installed:

Calendar 4.4
FAQ Manager by Iversia 3.2.0
Find Unanswered Threads 1.0.5
Join User Group by Waindigo 1.1.6
MattW Back To Top 1.0.3b
Members List by Waindigo 1.0.1
Moped Map 1.0.7
Post Ratings 1.7.2
ragtek Most Online User 1.0.0
Respollo 1.0
Sidebar Positions 2.1
Similar Threads 3.3
Sitemap for XenForo 1.4.2
TPU: Add Signature Pictures 1.0.0
TPU: Detect Spam Registrations 1.5.0
TPU: Detect Spam Registrations (Javascript) 1.1.0
User Criteria by Waindigo 1.0.15
WDB Popular Content 1.0.5
XenForo Media Gallery 1.0.1
[bd] Tag Me 3.0.5b
[MWS] Daily Statistics 1.2.4a
[XenMods] HashTagging 2.0 Stable
Thanks to your simple suggestion I found the culprit....

Member List by Waindigo was the culprit. Thank you @AndyB for also messaging me the suggestion to turn that one off first...he was right on!!