Okay.
First of all it's not a bug, I didn't realise you only just changed the schedule, so I will move this thread back to "Help & Support".
Secondly, I think you owe the Support team a big thank you because on a Sunday morning they have manually fixed your league.
Thirdly, there is a message with a red warning triangle in the "Edit League Schedule" screen which clearly warns you that changes to the schedule only take effect as of the next season...
EDIT: Posting at the same time as Bruno