The smaller blade consistently turns off after being inserted into the end of the larger blade. Not immediately, but after 30-60 seconds. Might be due to the button being pressed inside the larger handle, or maybe it's designed to do that as a battery-saving feature. But I doubt it was designed to turn off, since the larger one stays on.
It's poorly designed anyway because it looks small and weak. When you think 'double-bladed lightsaber', you thing of Darth Maul's, with the same size on each end. It's clear on the packaging that one of them is smaller, I just think it's silly. But one of our kids really wanted it for his birthday when he saw it in the store, so we got it. We were all pretty disappointed that the small light kept turning off.