Unfortunately the Memory Manager regards contacts as deletable if the space is required to keep the phone alive. DO NOT allow your phone to get below 12Mbytes free memory or there is a risk the MM will activate.
I can also confirm that Filters in the address book should all be cleared (unchecked) to see all entries. Otherwise only the entries which correspond to the checked category will be shown. The default for a new contact is to be NOT assigned to any category, so as soon as you set a filter (checked) the majority of your contacts are hidden.
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