Help with sound presets changing

Im new with OP-1 and Im having a problem with the sounds functions. After using it for a while (with the fx, lfo & sampler), the preset sounds/samples seem to change and I cannot seem to get back to the original sound I was using. I have to reset the op-1 in order for them to go back to where they were. Not sure if this is a bug or if I`m pressing some combination of buttons that alters sounds. Any help gratefully received.

Did you try with Shift+Synth (the blue sine waveform button)? This should go back to the preset