Genworth Financial Inc. shares fell 12% at midday Thursday after the mortgage insurer said it bulked up its loan-loss reserves as homeowners fell behind on mortgage payments. Genworth said it would post a net operating loss of 14 cents to 18 cents for the second quarter. Analysts had expected Genworth to post profit of 24 cents a share, according to FactSet Research. The stock tumbled to $8.30 in midday trades. In the pre-announcement issued late Wednesday, Genworth blamed “worsening trends” in its U.S. mortgage insurance business, citing “slow-moving pipelines of mortgages in some stage of foreclosure and delinquent loans under consideration for loan modification.”