Im puzzled by you temp results. Adding 168 deg F water to your 152 mash cant have resulted in a reduction of temp to 150. You have to of bleed heat somewhere or missed the number you expressed. Did you leave the cooler open bringing your water to 168 and your 152 temp was in fact lower? Did you lose a huge amount of heat transferring the 168, it would have to drop below 152 to reduce the combined temp? Point being, it isnt physically possible to add 168 to one 152 and reduce below 152. Depending of volumes if I were to guess, you should have hit upper 150s. You will want to know for future reference where you're bleeding heat.
Additionally, I dont understand the point of adding 168, it wont bring you up to mash out temps. You want to hit a combined 168 for the mash out, which means you need to add around 190 to boiling depending on the volume youre adding. You want to mash out for two reasons. First, it increases viscosity, which helps in lautering. If I was to bet this is were you got poor extraction, sugars didnt become viscous enough to drain, thereby leaving sugars behind. Second, the mash out denatures the enzyme activity, which results in setting your fermentability mixture. Second point would not have resulting in poor extraction.
Key take away, I would check BeerSmith. Did you misread the infusion step that 168 were your target for the mixture and you should have added water at a good amount higher?
Otherwise, all Ive got to add is to check water pH. Along with seconding aStoutObserver. Did you adjust for temp when taking the gravity reading; couldnt EASILY of been just a reading mistake as gravity goes down significantly with increased temp.