Hi, I have a new Harmony 890 that I am having trouble setting up. After setting up my devices and activities, the results were less than satisfactory. For example, it will turn on my tv but not my cable box. I followed the help screens and it fixed the problem. But, the next time I use it, the remote still won't turn on/off the box. I solved it again with help but the changes don't seem to stick. Why won't the remote learn its own fixes?

The "Help" button is used to re-sync device(s). It does NOT modify your configuration.
I see 2 possibilities to your problem:
1) You selected the option "I want to leave this device on all the time" in the cable box Device Adjust Power Settings. This option prevents the activities (including the special "Off" activity button) from controlling the power of that device. However, the activity "Help" feature still tracks what the power state should be and will send the power command when asked.
Solution 1: Select option "I want to turn off this device when it's not in use".
This is the standard option allowing the activities to control the power.
Solution 2: Select option "There are no power buttons...". You will have to control it manually.

2) The inter-device delay for the cable box is too short and it misses the power command.
Solution: Increase the cable box inter-device delay (Device > More Options > Adjust the delays).