In version 3.03 I have located a bug that prevents custom fields from being saved on product upload. The scenario is this:
1) Select Upload Ad - for a category that has several custom fields (I have tested only text fields)
2) Fill out the fields and submit
3) Resulting ad does not have the values entered displayed in the fields
Please note that this can be an intermittent problem...here is why:
In uploadproduct.php there are the following lines:
Content visible to verified customers only.
Nowhere in this file is $i initialized to a value. Given this it may equate to empty or a random value. In my case rather than showing up as empty (therefore enabling the following strstr function to operate correctly) $i is set to a random value preventing a match using the strstr function. This prevents the attributes from being saved.
In my case I removed $i from the above lines and the attributes/custom fields are now saved correctly.