I have the same similar issue as Heather Tillman that has been driving me nuts. I purposely installed a known working 3/4" NPT 24v solenoid on/off valve inline before my sprinkler manifold for safety. I too like Heather had/have a Rain Bird controller that I was replacing with your unit. I have the new HD-16 unit installed now. Originally I thought it might of been too high a draw amp wise on the common circuit because the Rain Bird only had one common wire for the 12 zones/valves I have. So, as an experiment I separated out the commons by running a specific separate wire bundle that just held commons, one wire dedicated per each of the rain machine HD-16 (3) Common outputs, plus 2 extra wires since it was a 5 wire bundle. The master valve is currently wired in on the 1st common along with the other 5 valves/zones. It has its own 2 wire setup where the common goes to the 1st common output terminal next to Zone 1 That common also is shared with Zones 2 thru 5 by tying a third wire used to join the two into one wire for the first common output connection. The other wire from the master valve is then directly connected to the Zone 1 output terminal.  (My old zone 1 is now in the zone 2 spot on the new controller, all other valves incremented by 1 as well to make room for the new master valve.)  I don't regret this because during the first test I had a pvc pipe weld fail on the manifold and the Master valve was able to stop it from becoming a flooding disaster. So, figuring hey dividing the commons should at least help....nothing. Same frustrating crap. I even purchased new rebuild kits for the valves figuring it was that they may be mucked up. Nope, they all were clean. 

Just like Heather (" Last Zone runs with every other zone ") my Zone 2 and Zone 7 like to stay on with the previous zone tested. Then they go on with the new zone that is in the cycle and off with it as well. It is like a software bug where when a user makes Zone 1 a master valve control the other valves latch open and close with the valves being tested regardless if it is a program, or one by one testing. 

If I test zones one by one the master valve comes on first 5 seconds before actuation of the Zone being called for, then it shuts off 5 seconds after that Zone cycle ends. I used the settings to put in the short delay to assure that the water flow would be at pressure at the valve when it opens, but immediately shut off once its job was done. I am totally perplexed over the fact that the testing of the zones also triggers other zones to come on as well. I am curious at what you found out. BTW, this is my 2nd HD-16 the first one exhibited the same issue.  Good thing I still have it because the replacement you sent had a bad WiFi antenna and I had to swap them out for the new one to work at all. I do need a new shipping return label for the old unit since my 4 year old decided to make art out of it while I was at work....

So, I await your thoughts and am willing to help solve this as it is really making me frustrated and mad because I don't have a lot of time to spend a whole weekend troubleshooting the issues mentioned above. My time with my family is limited due to work so, any help here would be appreciated. 

Thanks,

John

Please let me know if this is a systemic issue, or just a fluke that you hopefully have a solution to for us previous Rain Bird owners. I look forward to your reply.