@Arnd: Samer updated the UI/app script to not send the DC boost time variable for firmware 2.1.5, therefore, even if you haven’t upgraded your firmware, the bug is gone.
The reason to simply not send this variable is that firmware 2.1.5 has another bug, in that it ignores the DC boost time variable and uses a fixed 250ms instead. As a result, it doesn’t make any difference to change that variable at all. These bugs have all been fixed in firmware 2.1.6.
If you are wondering what role DC boost time plays: it controls how long the boost converter is turned on before opening each valve. The boost converter itself is set to a maximum voltage of 22V, so there is no danger in exceeding that voltage. But depending on the input voltage, the time it takes to reach that voltage may vary. For example, one feature of the DC controller is that you can even use USB power to drive the sprinkler valves (yes, you can try it, and it works). But USB power is only 5V, so it takes longer to boost that to 22V compared to a 9V input. In that case you may want to suitably increase the boost time to allow the extended charging time. The other reason to have a configurable DC boost time is that there are cases you might not want to enable the boost voltage, such as someone using a 12V power supply and drive 12V solenoids — in this case there is no need to boost the voltage to 22V. You can set the boost time to 0 to achieve this.
Now I think about it, it’s probably not necessary to have this as a configurable variable, and we may as well just remove it in the future.