Problem with DTPR

Hello!

I'm using a CYGNAL C8051F020 with the CYGNAL C8051F uVISION2 DEBUG DRIVER v1.29, Keil C51 V7.05 with µVision2 V2.37.

I've got a problem which I've isolated like this:
The command

MOVX @DTPR,A

writes the value of A both to the address specified by DTPR and to a address DTPR-0x1000, which in worst case contains any variable.
E.g. if DTPR = 0x12B9 the value in A is written to x:0x12B9 AND to x:0x02B9.
Can anyone help me? Thanks!

Astrid