Why is ":CLOCK => hh:mm" allowed as a clock entry?

[Marcin Borkowski <mbork@mbork.pl>]

Hi all,

I am studying the `org-clock-sum' function (I need to parse an Org file
and extract clocking data), and I noticed that ":CLOCK => hh:mm" is
allowed as a clock entry.  The Org syntax at
https://orgmode.org/worg/dev/org-syntax.html#Clock,_Diary_Sexp_and_Planning
confirms this.

What is the rationale behind this?  I want not only to sum the clocks
(org-clock-sum does that, of course), but I want more detailed
information (like how many clocks were that in the given period etc.).
The format with only the duration makes this troublesome, and I'd like
to ignore such entries (I have never seen them in my files, of course).
I'm wondering what scenario could lead to their existence?

BTW, the syntax draft says that there can be any TIMESTAMP object before
the DURATION, but `org-clock-sum' assumes that its timestamps are
inactive.  Isn't that a bug?

TIA,

--
Marcin Borkowski
http://mbork.pl