Hi Ioannis,
Mode 3 was added in September but it doesn't look like the help was updated, sorry about that. The operation modes are as follows:
1 - Startup mode, during hours when useful energy is collected and tank temperature is somewhat stratified
2 - Mixed Mode, during hours when useful energy is collected and tank temperature is fairly uniform
3 - Stratified mode, during hours no useful energy is collected and tank temperature is very stratified.
So, no the three value is not a bug. Your recent questions all make it clear that it would be beneficial to revisit the technical manual and work to get it published.
Thanks,
Nick