The default blend value of a blend tree node is different in the Animator windown and Inspector. The Animator window shows a generic "Blends", but the Inspector shows the first parameter, in this case "Speed". In order to set the blend value to "Speed" you will need to first set it to some other value and then back to Speed. In addition this makes it hard to eye ball what is wrong with your blend tree, unless you're aware of this discrepancy.