33CH DMA trigger select Datasheet and Watch

Hi,
working on MSI FIFO with DMA i found this:
- in the Family-Reference Manual DS39742B for DMA the DMA trigger is selected in DMAINTn: CHSEL<5:0>
- in the device spezific Datasheet DS70005319B it is CHSEL<6:0>, one bit more.
Of course the second is right. For the dsPIC33CH128MP50x for example the MSI Master Read FIFO Data Ready IRQ has a code of 0x53 which requires 7 bits.
Now -when I write 0x53 to the bits CHSEL<6:0> in DMAINTn and watch the DMAINTn in the WATCH windows it shows:
- a value of 0x5300 (as expected), but
- CHSEL = 0x13 (wrong)
(IDE 5.0, XC16 V1.35, PICKIT3)
Keep in mind: never trust the IDE.