Inserting Quote - Valid Until field does not update all other fields insert fine. Checked format is MM/dd/yyyy

Inserting Quote - Valid Until field does not update all other fields insert fine. Checked format is MM/dd/yyyy

Hello,

The following inserts a quote perfectly EXCEPT the field "Valid Until" (date) field is not inserting. There are NO ERRORS being thrown by the API.

I have tried the DateTime format also. We have other clients where that works fine but again datetime and Date are failing on this field, I have tried as CDATA as well.... I have confirmed from the UI the Spelling of the field as well as the fact it is indeed a date field (type is date)...

<Quotes>
<row no="1">
<FL val="Subject"><![CDATA[Amanda+Test+Price+Sheet+A]]></FL>
<FL val="Valid Until">03/03/2017</FL>
<FL val="Quote Stage">Proposed</FL>
<FL val="ACCOUNTID">[removed for security]</FL>
<FL val="POTENTIALID">[removed for security]</FL>
<FL val="Grand Total">118</FL>
</row>
</Quotes>


So to confirm, the new quote is created, subject is correct, stage is correct, account looksups correct etc. ONLY Valid Until is missing.