iPhone 4s won't automatically join known open wi-fi network

I have an iPhone 4s with the latest software update. Under settings>wi-fi>ask to join networks..  It is turned off.

If I am at home , the iPhone 4s will join my secured home network automatically , every time I walk in the door.

But, when I walk into work, it will not AUTOMATICALLY join an open unsecured known network.  I always have to go to settings>wi-fi>and manually touch "linksys" and it will join.

I have ran some tests with my iPhone and iPad side by side at work....

With both devices connected to the open linksys network, I will turn wi-Fi off on both devices, then turn it back on. The iPad will automatically rejoin the linksys open network every time, the iPhone does not automatically join. I always have to select it manually.

I have tried several remedies...  I have selected "forget this network", and then rejoined it.  I have reset my network settings. I have turned the "ask to join networks switch "on and off". And I have done a hard reset on the phone. All to no avail. Any suggestions???