I "think" if you go to the IPPIN entry box and right click and choose ADD NOTE then it will show up in the List of Notes in the Review Diagnostics that you look at prior to EFiling.  I know it creates a little pencil icon on that line, but Im with you, having it show up as a red error on the forms list would be great, same goes for SSA income, if they had it in one year, the next years program should flag it as a red error for missing info until you either enter a figure or remove the worksheet!