Return value of ReadChunkRecords()

According to autodoc, this function should never return 0. It is either positive number of records, or negative error code. In my program I read records in a loop. Assume my IFF file chunk contains 2 records and I read a single record 3 times. The third call returns 0, however I would expect IFFERR_EOC, as I attempt reading past end of chunk. Is it a bug, or my misunderstanding of documentation?