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The Do not search for an MT match when one of the selected matches exists option (Project Editor → General info → Machine translation) refers to only enabling searching for MT matches even when a given segment already has other TM matches. If you have, for example ICE and Leveraged options selected, then MT will be omitting those segments where ICE and Leveraged were first found, and will look for another segment where either the rest of TM matches are present or the segments are empty.
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