ultoa(), utoa() returns wrong pointer value (DTM)

XC16 v.1.31 (checked also with 1.20 and 1.26).Using: unsigned char conv={};
unsigned char *ptr;
unsigned long next_sn=1234;

ptr=ultoa(conv, next_sn, 16);

conv address is 0xC34 (checked with debugger) ultoa() returns 0x..