Hello Thomas,
Thank you for your post. I have been looking through it and I assume you have set the InvalidValueBehaviour property of the field which has a higher precedent than the one in the style and that is why such behavior occurs. Please note, we are making efforts to ensure all posts are addressed by an Infragistics expert. We believe that the other community members could benefit from this thread as well.
If you have any further questions on this matter do not hesitate to ask.