Adding hours/mins/secs etc to the duration does not add up correctly

axis2_char_t *duration_str = "P19Y6M4DT12H30M5S";
printf("input:%s\n", duration_str);
axutil_duration_t *duration = NULL;
axis2_char_t *result = NULL;

duration = axutil_duration_create_from_string(env, duration_str);
int hours = axutil_duration_get_hours(duration, env);
axutil_duration_set_hours(duration, env, hours + 13);
result = axutil_duration_serialize_duration(duration, env);
printf("result:%s\n", result);

The output of the above program should ideally be
input:P19Y6M4DT12H30M5S
result:P19Y6M5DT1H30M5.000000S

But it is actually is
input:P19Y6M4DT12H30M5S
result:P19Y6M4DT25H30M5.000000S

When hours exceed 24 it should be counted as 1 days and 1 hour instead of 25 hours. This problem is there for other time units as well.