Custom fields numeric conversion, delete failure

I have created a numeric custom field and when I set one record to the value of 5555555 then look at the result via api or web interface and the value turns up as 5555560.

I query the api for list of existing customfields and get this:
[{"uuid":"81c6df78-765e-4bc4-885c-203f5cc5010b","object":"job","display_name":"Property ID","field_name":"prop_id","field_type":"Numeric","is_unique":0,"sort_priority":0,"max_length":0},{"uuid":"96051471-5c35-48ff-b768-203f59a3303b","object":"company","display_name":"Property ID","field_name":"prop_id","field_type":"Numeric","is_unique":1,"sort_priority":0,"max_length":0},{"uuid":"fbbb2eee-3ead-414b-b51d-203f5401ecdb","object":"job","display_name":"Kowhai Lead ID","field_name":"quote_lead_id","field_type":"Numeric","is_unique":0,"sort_priority":0,"max_length":0}]

Immediately after I try to delete the fields and get this for each attempt:
{"errorCode":100,"message":"Invalid UUID"}
The DELETE method is called with payload of e.g. UUID=81c6df78-765e-4bc4-885c-203f5cc5010b as per documentation.