Must a C state transition function use palloc on the returned value?

Hi,

I'm defining a new aggregate using a C transition function. It is of
type TEXT, so the C function gets pointers (*text) to the internal-state1 and
next-data-item parameters. 

Question is if the returning value of type *text must be palloc'ed or
can be just taken from the input parameters. In the latter case I get
error messages like 

NOTICE:  PortalHeapMemoryFree: 0x0x40b22ce8 not in alloc set!

Dirk