The bug

Structure blocks cause block updates when loading the structure, even if the structure integrity is set to 0.

I haven't tested if it occurs when loading a structure void structure, but it may also be the case there.

Expected behaviour: non-changed blocksand "empty" areas give no block updates.

How to reproduce

1. Place a SAVE structure block and power it

   /setblock ~2 ~ ~-1 structure_block{posX:0,posY:0,posZ:0,mode:"SAVE",sizeX:1,sizeY:1,sizeZ:1,name:"mc-114396"}
   

2. Place blocks to detect a block update

   /setblock ~2 ~3 ~1 piston
   /setblock ~2 ~4 ~2 redstone_block
   

3. Place a LOAD structure block and power it

   /setblock ~2 ~ ~1 structure_block{posX:0,posY:2,posZ:0,mode:"LOAD",sizeX:1,sizeY:1,sizeZ:1,name:"mc-114396",integrity:0f}
   

   → You should see that the piston was updated and is not extended despite no block being placed

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

The method net.minecraft.world.gen.structure.template.Template.addBlocksToWorld(World, BlockPos, ITemplateProcessor, PlacementSettings, int) updates the neighboors of a block regardless of whether it was placed or not.