I have seen many similar issues but none that are quite the same.

You should be able to do this because placing other blocks replaces the light, including if it is in your off hand. In the case where a block is in your off-hand and a shovel or hoe is in your main hand, it doesn't make sense for it to perform the off-hand action when the main hand action is possible.

While this seems most like a bug to me, I'm not entirely sure if this is a bug, intended functionality or something of a feature request, but due to some right-click actions which invalidate the placement of the light still functioning, why shouldn't using a shovel or hoe?