Structure blocks incorectly create source blocks when loading

When a structure block loads a structure that has a water source with a sign adjacent to it, it improperly waterlogs the sign, creating a source block where there wasn't one before. 

In the picture below, the structure to the right is what was saved, to the left is what was loaded. Breaking and replacing the signs does not work, as breaking the sign creates a source block, and so the sign is simply waterlogged when being replaced.