Injector hose leaks when water pressure is low

After taking the machine apart because of a constant leak and putting it back together several times(thought the problem was fixed) I discovered by chance that the sleeve (part#ap249047) midway in the injector hose, fills up with water and overflows when someone turns on a tap or flushes a toilet during the fill cycle. It appears the lower the water pressure to the machine the quicker the sleeve fills with water(and overflows). This has only started last week . never had the problem before. any reason for this, and if I replace the nozzle and the valve, will this cure the problem?
What is the purpose of this injector hose? Why not put a solid closed connector between the two hoses? ED