How to make Mou.app maintain PDF vector images on “export to PDF”? Did OS X change the way it saves to PDF recently?

I like to write letters in Mou.app (my favourite Markdown editor). I love the combination of Markdown, CSS and PDFs for desktop publishing.

My letter template includes a PDF logo in the header area:

&lt;div style="width: 300px; margin: 0px auto 0px auto; text-align: center;"&gt;&lt;img width="300" src="logo.pdf" /&gt;&lt;/div&gt;

---

&lt;div style="float: right; text-align: right;"&gt;&lt;strong&gt;December 11th, 2013&lt;/strong&gt;&lt;/div&gt;

&lt;br&gt;

Dear Sir/ Madam,

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer scelerisque tristique placerat. Aliquam et purus viverra, aliquam felis a, aliquet urna. Mauris feugiat, nibh sed scelerisque varius, quam nisi aliquet lacus, non mollis nibh risus in mauris. Phasellus posuere libero in arcu consequat fringilla. Aliquam nulla eros, sodales nec neque ut, ultricies pulvinar sapien. Quisque vulputate nec mauris id iaculis. Donec tempus augue in libero mollis pharetra. Pellentesque tincidunt urna posuere, placerat eros vel, varius felis. Nulla elit lectus, tempus a sagittis vel, imperdiet eu tellus. Cras eget quam nisi. Integer ullamcorper posuere velit ut ultrices. Suspendisse luctus rhoncus aliquet. Sed tristique vel quam at tempus.

Etiam cursus massa nec ligula ultrices, vitae aliquet mi pretium. Phasellus vitae pharetra odio. Sed eget elit sit amet ligula tincidunt rutrum. Nulla commodo orci ornare, viverra enim a, vehicula nisl. Vivamus est quam, molestie posuere rhoncus a, tempus vel dui. Vestibulum posuere, magna non sagittis ultricies, enim nibh vehicula leo, sit amet suscipit elit elit at nisi. Pellentesque quis urna felis.

Yours sincerely/ faithfully,

&lt;br&gt;
&lt;br&gt;
&lt;br&gt;
&lt;br&gt;

**Signature**


The PDF logo is a vector image. In the past when I have exported to PDF from Mou.app, the final PDF maintains the vector logo. Today when I tried, it now turns the vector logo into a bitmap, which makes the new PDF look really poor and ruins any prints that are made from it.

I don't think Mou.app is at fault as it hasn't been updated for a while and I was successfully making vector logo PDFs after Sept, 2013. Also, I get the same problem in Marked.app. This is why I suspect OS X Mavericks. Any thoughts?
I found a fix of sorts. Using a high resolution TIFF in place of the PDF logo improved the final PDF quality. Tried high-res PNGs, but the results weren't as good as a TIFF.