vpi_put_value does not assign value to a vpiPartSelect

[Henry]

Hi, All

I have a vpi task that takes a reg and assigns a value to it. The
parameter inside the task appears as vpiReg, everything is cool, the
reg gets it's value.
But when I pass x[0:31], the parameter appears as vpiPartSelect, and
vpi_put_value doesn't assign a value to the selected part of the reg.

Does anyone have any idea why vpi_put_value doesn't work for
vpiPartSelect? I use modelsim 5.5

Thank you for your help

Henry