$8M Housing Tax Bill For a Compluter Glitch

The story about the House valued accidentally at $400 million causes problems [News Sentinel] was a simple compluter glitch gone bad.

The homeowner of this house [NWI Times] got an $8M tax bill when they usually pay about $1,500 because the property was erroneously appraised for $400M [Chicago Tribune].

Thats not the story.

How did this sort of thing slip through the system? It seems like very little budget or financial oversight in this process was involved.