What was the problematic aspect of the Compromise of 1850?

Texas would relinquish the land it was arguing with Mexico over but would receive ten million dollars in compensation (which it would use to pay off its debts to Mexico); the slave trade would be abolished in Washington, D.C., though slavery itself was still permitted; California was admitted as a free state; and the Fugitive Slave Act, which punished people harboring fugitive slaves and allowed for the return of those slaves to their masters was passed.