[quote user="Matthias Lasch"]What I can see is that variables len and timestamp are both located in Register R9.[/quote]It looks like you may have found a bug in the MSP430 v4.1.5 compiler. Can you post your complete CCS project?
(I did create a test program with the code fragment shown but couldn't re-create the problem)[quote user="Matthias Lasch"]Nothing selected for optimization levels.[/quote]The default is optimization level zero, which can place variables in registers. If you set CCS Project Properties -> Build -> MSP Compiler -> Optimization -> Optimization Level to "Off", which will disable all optimization, does that make the problem go away?