Automatic Transmission out of gear on 2000 Volkswagen Jetta TDI

My 2000 Jetta TDI has an automatic transmission and after the engine and tranny get warm, it cames out of gear when you come to a complete stop. Get back on the throttle, goes back into gear. Once you are rolling, it shifts great and has no problems. Any ideas?

2 answers
It has low line pressure due to valve body problems beyond belief. It is well on its way to failure. Change fluid and filter and ensure proper fluid level but slim chance of curing it. Fordmotorandy@gmail.com if interested in a transmission.
my car did that for alittle while now it will not shift at all.any ideas