has_parent() oddity

has_parent() is a bit confusing to me. If one looks at the following two 
articles in news.software.readers with slrn v1.0.1:

<[email protected]>
<[email protected]>

they get threaded together. Neither article has a References: header.

Yet has_parent() returns 0 for the former article and has_parent() 
returns 1 for the latter article.

call("get_parent_header") on the latter article raises an exception -- 
"Article has no parent reference." -- which makes sense from the lack of 
a References: header but it remains unobvious why has_parent() ought to 
return 1 for 
<[email protected]> (I'm 
talking about the intention behind has_parent() not necessarily its 
current implementation).

It seems to me that if has_parent() returns non-zero, one ought to be 
able to identify the article that is that article's parent, even if that 
article is not present on the server.

I'm not sure if I'm seeing a bug in the has_parent() implementation, a 
bug in the has_parent() documentation (maybe more explanation about how 
has_parent() can return 1 even if the parent is due to slrn grouping 
articles into threads by sorting?), or if I'm misunderstanding something 
about proper use of has_parent().

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