Still present in 1.21.0
This bug seems like a bandaid solution to another bug but for some reason has been kept in the game for years now. Sometimes when bridging with the old behaviour in the old versions or with my DLL injected you can notice that even though you are in the continuous placing mode the block placing speed is capped and it doesn't keep up with your running speed. For that reason you need to restart your bridge again to remove the placing speed cap. That happens very rarely and it's actually very hard to reproduce. The lazy solution for this problem is just to place two blocks every time which the developers seemed to like for some reason.
I can confirm the issue. It seems like it only affects laptops with both integrated and dedicated GPUs. The issue is renderdragon specific because it doesnt occur in the older versions with the old engine.
the function which is responsible for placing blocks gets called for a second time if some condition is met. removing the condition eliminates the bug.
in this video I inject a small DLL into the game which does precisely that. it's just one line of code I am sure you can fix it
since the newest x86 builds now have renderdragon this bug should be prioritized to be fixed
Still present in 1.21.2