Last week we had a strange issue with one of the users. She used a simple SharePoint application that includes a People Picker control to enable users to assign items to other employees.
A pre-defined user should have been selected as a default value in the field via server side code, however it was empty on page load in this case. If the user typed the name or login name of any employees in the text box, the name was not resolved by the control as expected, although as we checked the network traffic by Fiddler, we saw that the request for name resolution was sent to the server and the server responded with the resolved entity. If the user tried to select the assignee via browsing the entities, she was able select the employee, but as she clicked the OK button in the Select People and Groups Webpage Dialog, the selection was lost and the text box remained empty.
Other users (using the same browser version, Internet Explorer 9, and having the very same permission on the system) had no problem with the application.
Fortunately, I noticed an unusual icon near to the URL in the browser, saying “Some content is blocked to help protect your privacy”.
As I found out, it was a result of the user activated unconsciously the ActiveX Filtering feature in her browser.
The solution was turning off ActiveX filtering for the site, however, one can turn off the whole feature, if it is not needed.
I was able to reproduce the issue when working with SharePoint 2010 up to the Internet Explorer version 11. In case of SharePoint 2013 the issue seems to be fixed, at least, I was not able to reproduce it with IE 10.