Problem with (Zotero-)BibTeX-keys

Zotero (http://www.zotero.org) constructs BibTeX-keys like this:

```
[name]_[first word of title]_[year]
```

Consequently, BibTeX-keys of works without author are exported by Zotero beginning with an underscore. This results in MultiMarkdown-citations like this one:

```
[][#_frei_2009]
```

These don't go down well with the parser. When trying to convert them to LaTeX, they produce errors like these (thrown by the MultiMarkdown-version included with Scrivener 2.0.2):

```
-:502: parser error : Unescaped '<' not allowed in attributes values

(<
^
-:502: parser error : attributes construct error

(<
^
-:502: parser error : Couldn't find end of Start Tag a line 502

(<
^
-:502: parser error : Opening and ending tag mismatch: span line 502 and a
(frei2009
^
-:502: parser error : Opening and ending tag mismatch: p line 502 and span
ass="externalcitation"> (frei2009)
^
-:502: parser error : Opening and ending tag mismatch: li line 502 and p
ef:fn40" title="return to article" class="reversefootnote"> ↩

^
-:502: parser error : Opening and ending tag mismatch: ol line 422 and li
n40" title="return to article" class="reversefootnote"> ↩

^
-:505: parser error : Opening and ending tag mismatch: body line 27 and div

^
-:506: parser error : Opening and ending tag mismatch: html line 5 and body

^
-:507: parser error : Extra content at the end of the document

^
unable to parse -
```

Could these be fixed? Or does the Zotero BibTeX-translator have to be modified? I don't think a BibTeX-key starting with an underscore («_») is invalid, though.