This issue affects both 1.12 and 1.14 and all spawning shapes except for spread. It makes blocks spawn particles closer to negative values of X: this is caused by the code subtracting 0.27 from the x coordinate of the particle when spawning it.
Status
Fixed
Type
Product/platform
Not applicable
Priority
Normal
Issue description
You are correct, I don't know why these offsets even were there hehe :D Thank you for letting me know and for extensive report and demonstration, this helped isolate the cause quickly.
You were just in time, I will fix this in 2020.2.