Tried it. And yes it does not work as intended. When I set for example LEN to 32 I can manually change to the next pattern after those 32 steps are played. But in Chainmode or in Songmode it doesn’t work at all. You cannot leave the pattern. This is not intended and therefore buggy behaviour.
Workaround for now:
(Copy your pattern and) set master length to any different value up to 1024 to set after how many steps it should go to next pattern of chain. For example, if one track has 7 steps and all the others have 64 steps your LEN should be 448 for a smooth transition to the next pattern. 448 is 7x64