The Status N/A when turning On a Scene is also what happens on my system. For an individual device the display shows the percentage of ON. With a Scene likely representing more than one device, although not a absolute requirement, it would not be possible to display the percentage of ON for each of the 8 different devices in one of your cases, for example. For OFF, all the devices are OFF so that works. Status N/A is representing something other than all OFF. Perhaps another approach could have been to display N/A for the percentage but show on when the last click was on. Something you could suggest under the new features Topic.
When you select an individual device and click ON/OFF, an Insteon Direct command is sent to the selected device. A Direct command does not utilize a Responder link record in the individual device. For a Scene ON/OFF a Group command sequence is issued which requires a Responder link in each of the Responder devices to tell each device how Bright, and how fast (Ramp rate) to get there. Sounds like something is wrong with the Responder link in the 8th device. It could have a Bright level so low as to look off when it is actually on very low. It could have a ramp rate so long that it looks like it did not turn on when actually it is taking several minutes to turn on. There could be other problems as well.
I would like to use the SImpleHomeNet Utility Suite as a independent tool to view the Responder link records in the 8th device. DId you get that program working? If so I will walk you through the process of displaying link records. If not then use EZSrve under Device Management and do a SYNCH EZSERVE for the device that does not respond to the Group. This will read the device link database and rebuild the link information in EZSrve. Look at the Responder link and see what the various values are.
You are making good progress. Almost there.
EDIT: when looking at the link information after the SYNCH EZSERVE, also look for a duplicate entry. You may have an old link entry in that device with LD1-3 values that do not match the last Responder link you created.