Huion Kamvas pro 13 function button error

Since i bought this tablet, i noticed that sometimes, for no reason at the moment, the function button setting were changing. I like it in change brush size, but sometimes i was drawing, using it like always, but from one moment to another, the bar function setting changed and now is in move camvas up and down or in zoom. It wasnt a problem at the moment, it was something rare, and it only took 2 button presses to come back to were i like it. 

Now, i changed my buttons function and one of them its used to go back in the history (in photoshop) and, being that its function, i use that button a lot. Well, i dont kow if its the button or what ( if you want to know, its the third one, the one after the brush size, zoom... control bar), but, i dont know why, sometimes changes the bar function. Im going to put it in situation: i need to go a little back, i press it lets say 5 or 6 times, well, one of those time, i dont know why, changes the bar function, and no, i didnt missclicked the function button or something like that. Now imagine that, but in a long drawing session, where im going back a lot of times, its just stating to be really frustrating and bother me a lot.

Btw, i got the lastest drivers, i didnt change anything important in the drivers settings, just the buttons function, and, literally, i never press the function button in a "voluntary" way,  i mean, i never pressed it, beacuse i wanted to use another function in the bar, always because i want to change where a like it, so its a button that for me would be better if it was blocked. 

I want to know whats the problem, if it has a simple solution, if i can do something, or if i can simply block the bar function where it is and leave it there forever, even if i press the function button.