Why has my tub spout diverter not dropping back down after use? (brand new installation)
When the faucets are turned off when you are finished showering the diverter will usually not drop by itself.  The diverter is held up by the column of water in the shower pipe. Once the column of water is reduced due to dripping of the diverter, the diverter stem will fall and reopen the spout to its normal position. How long that takes is dependent on how long it takes for the column of water in the shower pipe to fall. I usually just push down on the diverter actuator pin to release the shower pipe water.