If the button is currently animating when it gets disabled it breaks. Adding this fixed it for me:
void OnEnable(){
buttonDown = false;
}
You probably want to run some cleanup too, to ensure your buttons appear correctly after the disabling if you do any sort of scaling. I ended up just writing my own button script (I'll share it eventually, not in a great state atm though - and it depends on the "FingerGestures" plugin anyway).