Attempting to add a Filter (or possibly ANY transform) before Flatten transform will break IMan.

Let's say we have a Magento Reader with a 2-level dataset (Order Header and Order Detail) and then a Flatten transform.  Flatten the 2-level dataset into 1-level.  If you try to add a Filter between those two levels IMan will freak out and break the link between the Magento Reader and the Flatten transform.  It does this because the Flatten transform now only consists of 1 level while the Reader and Filter are 2 levels.

I understand if it's a bug that IMan can't figure this out, but at the very least it should fail gracefully and not break the existing link.  Luckily I know how to modify the XML directly, but for someone who didn't know how to do this, it could take them HOURS to rebuild the job if it's complicated.  And if they don't have a backup of the job, they are screwed.