We’ve never seen, nor heard any reports of a problem like this. As you mentioned, simply deleting a field definition should remove the field value from message objects that have a value defined – nothing ‘bad’ should happen.
Despite the fact you are using Formativ, you are actually using the native GroupWise Object API here. Formativ doesn’t provide any additional ‘wrappers’ or functionaility in this regard. When you access something like GroupWise.Account in Formativ, you are using a native, unmodified Object API object. Without wishing to appear evasive, I am extremely confident any issue in this regard is not related to Formativ. It is almost certainly an Object API issue, or an issue with the GW agents being used.
Which version of GroupWise are you using? As MA alluded to, some earlier versions of GroupWise didn’t handle the management of custom fields particulary well. Nothing destructive that I am aware of, but it was certainly problematic to delete field definitions, etc. It may be worthwhile upgrading to the latest services packs, etc, for the version you are running.
I can’t really provide you with any other advice, other then try increasing the size and traffic on your development system and try again. I would also ensure your live system is fully patched and completely ‘healthy’ before adding the field definition again.