It is possible that the devices are not correct if the DevClusters.xml file was not correct at the time the devices were added. It is the DevClusters file that provides the correct model for the device characteristics. If the DevClusters file was not correct I would delete and add one or two devices and see if that resolves the GUI not showing correct device status for those devices. You might try clicking on the Refresh button before doing that to see if the status is known, just not being displayed.
However, even though my GUI display is showing the correct device status after an On, I see the same thing here you are seeing with a SendInsteon xml command and my DevClusters.xml file is correct and was when my devices were added. The SendInsteon command to an ICON Switch works, but to an ApplicanceLinc and a LampLinc it fails. Both the ApplicanceLinc and the LampLinc are responder only devices which may explain why they fail and the ICON Switch works. The Query command is actually being issued and ACKed but incorrectly posted as failed in the xml response. I sent a note to Simplehome yesterday documenting what we both are seeing regarding the SendInsteon xml command. I was able to get the LIST FILES on IE8 to work by setting the Compatibility View option for all applications.