Is the hot water supplied by a central water heater or do you have your own? If it is a central unit then it could cause the problem but it would more likely be a valve in someone else's unit. If you have an individual heater then it would not inject hot water into the cold water sysstm unless the water was being used elsewhere in the unit, which does not seem to be the case, since you say it happens when you open the faucet, not after it has been flowing for a while.
: I think that it may be my condo causing the problem. I am pretty sure that they only replaced the cartridge, not the valve itself. The valve could create that problem though? Thanks.