Citation-number variable in citation is incorrect when additional items are manually added to bibliography (through "Edit bibliography").

Example:

<citation et-al-min="4" et-al-use-first="1" collapse="citation-number">
<sort>
<key macro="language-sort"/>
<key macro="author"/>
<key variable="issued"/>
</sort>
<layout prefix="[" suffix="]" delimiter="; ">
<text variable="citation-number" suffix='. '/>
<text macro="author"/>
<text variable="locator" prefix=", с. "/>
</layout>
</citation>

<bibliography et-al-min="4" et-al-use-first="1">
<sort>
<key macro="language-sort"/>
<key macro="author"/>
<key variable="issued"/>
</sort>
<layout suffix=".">
<text variable="citation-number" suffix='. '/>
<text macro="author" />
</layout>
</bibliography>

Results:

citation
[1. Nagel T.]

bibliography
1. Gross D.K.
2. Nagel T.
3. Sahlin B.H., Harding M.G., Seamon J.G.

Two items are manually added: "Gross" & "Sahlin et al.". The items in bibliography are sorted alphabetically, so Nagel's paper is the second, but citation-number still shows 1.

Is it a known bug and is there any fix?