Checking for uniqueness of fields even after one of the fields involved has failed validation

I've got a content type that uses a combination of 3 fields for its uniqueness check.
One of them is an integer field.

If you put letters in this integer field (called Project Number in this case) it fails validation and you get the following messages:

"Only numbers are allowed in Project Number"

"Could not formulate query for unique_field_match_value on field_project_number with data type int."

"Warning: array_intersect(): Argument #2 is not an array in unique_field_nodeapi() (line 209 of /var/www/sites/all/modules/unique_field/unique_field.module)."

I think this may be because unique field is testing the node uniqueness even after the node has failed to save due to the integer field having letters in it and as such there's a data type mismatch in the query involved.