The rate of St. Louisans behind on their mortgage topped 6% in February, even as the number of people actually facing foreclosure stayed relatively flat. New figures out this week from First American Core Logic show a rising tide of people facing mortgage trouble as the weak job market drags on: 6.1% of St. Louis-area borrowers are at least 90 days delinquent, according to the real estate data firm. That’s better than the national figure of 8.78%, but it’s also up markedly from the same month last year, when 4.1% of mortgages were in default.