No it doesn’t require firmware update — it’s a bug in the preview scripts on the server. We’ve already worked out the fix and it should be released very soon. Samer can probably give you a better idea of exactly when.
Just to summarize this thread and the relevant thread from the support ticket: the issue is caused by the preview scripts not properly handling programs that repeat too frequently. Here ‘too frequently’ means the program is set to repeat at an interval that’s less than the time it takes to finish the program. For example, if a program takes 30 minutes to finish watering all stations, the interval to repeat this program should be more than 30 minutes. If the interval is less than 30 minutes, it’s trying to reschedule the program before it can finish the first pass. In this case the firmware can handle it correctly (i.e. meeting the sequential requirement); but the preview scripts are not completely consistent with the the firmware, and show stations running in parallel.
In any case, the preview issue is fixed and will be updated soon. We will also soon add a checking of the program interval setting to throw out a warning if the interval is set too short.