offset for file opened in append mode

The offset for a file opened in append mode seems to count from the end of
the original file, rather than the start of the file:

Version 5.1.0, Wed Nov 22 12:31 2000
[eclipse 1]: open(file, write, a), write(a, hello), close(a).

[eclipse 2]: 
[2]+  Stopped                 eclipse
holborn: more file
hello
holborn: fg
eclipse
open(file, append, a), get_stream_info(a, offset, Z), at(a, Y).

Z = 0
Y = 0
yes.

The offset should not be 0 here if counting from the start of file...

[eclipse 3]: write(a, there), at(a, Z).

Z = 5
yes.
[eclipse 4]: close(a).

holborn: more file
hellothere

The output is correctly appended to the end of the file. Should the offset
be counted from the start of the file, rather than the original end?