ePub 3 weird results when converting to mobi

Good afternoon:

I was able to validate the book I'm working on. Now when I use Kindlegen to convert to Mobi I get multiple errors like the ones below

     [exec] Warning(inputpreprocessor):W29007: Rejected unknown tag: <abbr class="acronym">

     [exec]       in file: /var/folders/jz/_pr7872j2jx765_7lyh3z__07x_v0x/T/mobi-ZpXrJk/OEBPS/ch04.xhtml     line: 0000038
     [exec] Warning(inputpreprocessor):W29004: Forcefully closed opened Tag: <dl>
     [exec]       in file: /var/folders/jz/_pr7872j2jx765_7lyh3z__07x_v0x/T/mobi-ZpXrJk/OEBPS/ix01.xhtml     line: 0000002

     [exec] Warning(inputpreprocessor):W29004: Forcefully closed opened Tag: <dd>
     [exec]       in file: /var/folders/jz/_pr7872j2jx765_7lyh3z__07x_v0x/T/mobi-ZpXrJk/OEBPS/ix01.xhtml     line: 0000002
     [exec] Warning(inputpreprocessor):W29010: Tag rejected due to being used in unauthorized scope: <dt>

     [exec]       in file: /var/folders/jz/_pr7872j2jx765_7lyh3z__07x_v0x/T/mobi-ZpXrJk/OEBPS/ix01.xhtml     line: 0000002

I remember that late last year this also came up but was not able to find a resolution. 

I am using the kindle.extensions parameter and can copy my customization layer if needed. 

Any idea of what I'm doing wrong to generate the extraneous code?

Carlos