Tools Transparency Object (1) not working correct

I do not understand working Transparency Object (1)

After Photoshop experience, I expect to set the transparency of the object, but once I set it to a value, eg 30, but then return it back to 0, the object stays clear with the 30 setting.

Is this a standard behavior?

I use this if I'm trying to photomontage and need to put two objects exactly above each other.

Thanks your help.