Depending on your GT's age, it may come with one of two types of switches. If the GT is set up for the wrong type of switch, you can see odd things happen. For example, buttons will trigger when you release them instead of when you press them.
To get the GT to scan the switches and automatically configure itself for the switches it finds connected, power up the GT while holding the right hand side black button under the main screen. Keep holding until all of the displays light up. Only hold that one button, nothing else. Once all of the displays turn on, it's set up.
There are also a few other possibilities. The GT has a lot of configuration options, and many of them can change how the buttons operate. An incorrect configuration can result in unexpected button behavior. The easiest way to figure out if it's a configuration error is to enter setup mode by holding the two small black buttons under the main screen. Once in setup mode, press the button(s) in question. If they function correctly, it's likely a configuration error. Setup mode always works the same way, regardless of your configuration settings.
If neither suggestion helps, your switch may bee to be replaced. They are user-replaceable, no soldering required. Or, you can contact us to arrange a repair. If you choose to replace them yourself, you can buy switches here: