Block (such as stone or grass, but not limited to) changes when entity is placed on it.
What I expected to happen was the block (it was grass and sand block that i saw it happen on twice in a 5 minute period)
to not change.

What actually happened was transformed, if you will, to a different entity. I was a little frazzled when it happened the first time.

1.not possible to tell an exact step by step but, i placed a railroad track (i also did a switch and a red stone piece) on the grass block (it was in the swamp but it doesn't have to be)and it changed to sand