Thanks for your comment. It was my crazy error! 

@vv 

Thanks! That is what I got, when testing this command with Maple 2019.
Did you use newest version of Maple?

@dharr 
Thanks dharr,
Do I understand your answer correct, that Maple 2023 returns the list [-1,0,2]  as well, if you define the function piecewise with f := x -> piecewise(-1 <= x and x <= 2, x^2, undefined) ?

Thanks Kitomnum, 19295, that improves my knowledge about the options of dealing with log functions.

Thanks tomleslie. As you can see from my question I used "with(RealDomain)" and with Maple 2019 I received for x=2 "no undefined". It is obvious that both log[2] terms (right and left hand) are complex with x=2. If you prove the solutions, you must substitute the values into the original function and that gives you on the left hand and right hand complex numbers. Sure: If you transfer the log[2] expressions to one side and write it as a quotient in log[2] you will get a positiv result and two real values as solution. I suppose, that is what Maple 2019 does. Your calculation is with Maple 2022. May be, that this issue is a question of the Maple version?