But, what I mean is, that scale (150,40) seems to apply to any button I create with Widget Tool > Template 'Button', even if I choose a background that is not 150x40, that's why I thought (150,40) was something on purpose or default or something like that.
It'd be ok if I then manually set the collider and sprite (background) scale to its actually size but this is happening everytime I create a widget button in any panel of any UI. Maybe there's something wrong being set in my project, anyway still hope someone already had and solved the similar issues.