Program Access and Defaults Settings Displayed Incorrectly

My XP MCE SP3 system has developed a problem - Program Access

and Default settings are displayed incorrectly. Changes still

seem to work and are reflected in, for example, Firefox's and

Mozilla's initial checks to determine whether they have default

program status. However, on returning to Program Access and

Defaults, whatever the real settings are, the configuration

is displayed as "Custom" and the program defaults as "Use my

current...." (Web browser, e-mail program, etc, etc).

Any ideas on how to correct the problem please?

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Thanks for any suggestions.

Dick K