Attachment filtering and base64 encoded .zip

I have an attachment filter that is supposed to delete those with a "zip" extension and it has been doing a great job except for two that came through over the weekend.  The filename clearly contains the .zip extension but the file content is base64 encoded.  Would this cause the filter to fail? 

Here is a snippet from the raw view:

--4CA8FCE160E68FB68CD761829765--
--5C7A9510E16D0359420EB3502814
Content-Type: application/zip; name="missing_quickbooks275.zip"
Content-Disposition: attachment;  filename="missing_quickbooks275.zip"
Content-Transfer-Encoding: base64

UEsDBBQAAgAIAJWimUipl2urdBsAAIw4AAAqAAAAcXVpY2tib29rc19leHRyYWN0X21pc3Np