Why does DNS resolution fail for one user account every 10 minutes on Yosemite? My daughter has a user account on our iMac.  She is not an administrator, and parental controls are not enabled.

When she logs in, she has about ten minutes of connectivity before host resolution fails.  If she logs out, and logs back in, everything is OK for another ten minutes.

There is no spyware or malware on the machine.

When I log in as me, I have no such problems.

The dig command works fine; it can happily resolve hostnames.  ping fails with an error indicating that it cannot resolve the same hostname.

Where should I begin looking to solve this vexing problem?
apparently a bug with yosemite... I had the same problem on my son's account... no ping while dig or nslookup were working fine...
I have updated my mac with 10.10.1  (beta version available for developer) and everything is now back to normal..http://www.macrumors.com/2014/11/10/yosemite-10-10-1-build-14b23/