win.length got wrong result while using pattern in EPL Nesper

I have problem with windows length.

My condition: 1-Output will trigger if event happen within length 3 2-Output dismiss if event happen after length 3

Example: Event Sequence: 1:A 2:B 3:C 4:D 5:E 6:A 7:C 8:D 9:E 10:F 11:B Event Rule: Z = A --> B Expected Output: Z will occurred at index number 2 since win:length(3)

My Problem: The output Z also triggered at index number 11 eventhought it exceeds win:length(3)

My simple code:

"SELECT a.index, a.event FROM pattern [every (a=EventList(event=A) -> b=EventList(event=B))].win:length(3)"

May anyone help me to figure out how to to solve this problem? Thanks in advance.