I think we have found your problem.
You said you had X1-7 and Y1-4, in the 505 plcs, the X's and Y's occupy the same block of memory. There isn't X memory and Y memory, there is X/Y memory.
What does this mean? It means X1 and Y1 occupy the same physical memory location, that's why you cannot have an X1 and a Y1. When X1 is true, a 1 is placed in the image table, at the end of the scan, the PLC see's a 1, and energizes Y1.
You will have to reconfigure your I/O, start your X's at 1 and your Y's at 101 or something else not assigned to the input card, your problem should go away.