Header attribute doesn't work inside blockquote

[rgaiacs]

Steps to Reproduce

$ pandoc --version
pandoc 1.13.1
$ cat sample.md 
# Title Sample {.my-title-class}
$ pandoc -f markdown -t html5 -o sample.html sample.md                                                          
$ cat quote-sample.md 
> # Title Sample {.my-title-class}
$ pandoc -f markdown -t html5 -o quote-sample.html quote-sample.md

Actual Results

$ cat sample.html 
<h1 id="title-sample" class="my-title-class">Title Sample</h1>
$ cat quote-sample.html 
<blockquote>
<h1>Title Sample</h1>
</blockquote>

Expected Results

$ cat sample.html 
<h1 id="title-sample" class="my-title-class">Title Sample</h1>
$ cat quote-sample.html 
<blockquote>
<h1 id="title-sample" class="my-title-class">Title Sample</h1>
</blockquote>

[rgaiacs]

@jgm Thanks a lot.