Is it a bug?

[Antifaz]

I can't upgrade the majestic defense, majestic tree page 4
it is able to increase the defense but it suddenly appears a window with this message

[Reyco]

It is normal. you must distribute the points that these skills ask of you. And some will tell you that you reached the maximum limit. It all depends on how you distributed the points and also on the level you have