Off day changed at employment term, the off day at schedule for previous month changed too!

Staff A
Jan-May the off day was set to Thursday
I created another entry in employment terms starting June off day = Monday

When i go to Leave Schedule to view, all the off day in Jan-May changed to Monday!
Since I created 2 entry at employment term jan-May off day = Thursday, only starting June the offday is on Monday why the leave schedule show all off day = MONDAY?

Please help