This is right out of Microsoft's own official documentation. They are so busy off inventing the next latest change to the user interface that no one asked for that they can’t be bothered to stop and fix things that have been broken for years. There is a cultural problem at Microsoft that stems directly from it’s founder.
"Issues with the AutoComplete cache
This section describes known issues that can occur with the AutoComplete
cache. The AutoComplete cache can become corrupted over time and may not save
new entries. If this happens, you can try to remove individual entries from the
list. To do this, see the How
to remove AutoComplete list entries one at a time section. If that doesn't
resolve the issue, the whole AutoComplete list can be reset. To do this, see
the section titled "How to clear the whole AutoComplete list." "
