Red sand turns to normal sand on piston (sometimes)

On a server, I have a double piston extender with a quartz block at the top with a block of red sand on top of that. It's a gate that is connected to a daylight sensor. The pistons both raise the quartz and sand, then drop when morning hits. After a few nights, the red sand will turn to regular sand (hasn't happened in front of me).

What I expected to happen was...:
The red sand wouldn't turn to normal sand.

What actually happened was...:
The red sand turned to normal sand.

Steps to Reproduce:
Difficult to reproduce. Could be latency sending a goof-up between the client and the server? Not sure. The only steps I could recommend is building a vertical double piston extender and set it on a pulse generator, and just wait I suppose.