I wrote a module with a header_parser hook. If the post has a max Size I did like to tell the client "403 Forbidden" instead of "100 Continue". I found out that in modules/http/http_filter.c the 100 Continue handling does not look the return code. It tells the client 100 Continue all the time no mather wath may handler returns.
*** This bug has been marked as a duplicate of 43711 ***