Plugin encodes only part of post

I have a post with 18 mailto links and I noticed something odd. All of them get ROT13 encoded, but 6 of them are also still visible in the source.
It seems that those that fail to be completely obfuscated have the following format in the post:

</span><span style="color: #0000ff;"><a href="mailto:[email protected]">[email protected]</a></span><span style="mso-fareast-language: en-au;">   </span>

This gets translated into the following on the page:
</span><a style='href: "mailto:[email protected]"'><span style='FONT-FAMILY: ; mso-fareast-font-family: "Times New Roman"; mso-fareast-language: en-au; mso-bidi-font-size: 11.0pt'><font style="COLOR: " color=#0000ff><script …
.. followed by the correctly encoded email.

Appreciate your comments on this.
Cheers,
Jens

https://www.ads-software.com/plugins/email-encoder-bundle/