Shower Drain Puzzle?

[DD716TED]

I have one of those shower drains that when you push it down it locks in place and fills the tub.. to empty the water you again push the drain it pops up and the tubs drains.. Now the mystery begins.. When you take a shower, the drain is up however the tub starts to fill up (no draining).. Until you push the drain down to close it, then push it again to let it drain.. Now the tub drain works normal.. I have replace the installed rubber gasket/sealer in the pop up drain but no change.. you still have to push it down to seal the tub and then push it agin to pop the drain up to get the tub to drain when showering. All other drain lines in this bathroom (Sink / toilet) work fine so I have ruled out a vent issue.. IDEAS?

[akaothermick]

That sometimes happens when there is a clog in the drain, unscrew the pop up and remove any clog underneath it,