Observer returns signals and locks button

When building a tower of observers to carry a redstone signal upwards, I discovered that the button at the bottom gets locked and the redstone signal is locked by the first observer. You hit the button, and the power stays on in the lower circuit.

The attached images shows my test setup with both a half slab stair, and an observer tower. The obsever and the half slabs all have redstone on top of them.

The first two images both towers are connected, and shows before and after pushing the button. The next two images show before and after when only the observer tower is connected to the button.

The same behavior occurs in both cases. The signals goes to the top, as expexted, but then the button gets locked with power at the bottom. It never releases.