You have possibly 2 issues
1 When you program the the PDKU in front of the IVP 8 your ports shift off by 8 ports which will change all of your programming for the IVP 8 just as the previous post have mentioned

2. You can have only 28 station ports on a 40i
8 Base Cabinet
4 Single lines in the Base
4 KCDU Station Card
8 PDKU Station Card
8 IVP 8 (RSTU =8)
32 ports total