You indicated that the integrity check is clean. Likely this scenario is not checked for, as home currency accounts do not have currency records.
Normal processing should not have source and home currencies different for the home currency. I presume this is a balance sheet account, because income statement accounts would reset at year end. If the account does not have the MultiCurrency option selected, then this scenario is impossible - unless this account used to be a multicurrency account and was 'repaired' to not have this option.
If this account is a multicurrency account, there will be a multicurrency record for every supported currency for this account. The Net Changes for every fiscal period should match home and source.
If you wanted to search for the potential cause, and you have GridView and keep enough years of detailed history, you could create a View and filter for just that account and where the source and home currency amounts are not equal. If the detail still exists, you can find your answer.
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Regards,
Softrak Tech Support