I am using CP 4 rc3. I was told there was a recent change that checks on assignment for high-order bits truncation. The EPD library used to do & 0xFF when assigning to a buffer item, but that was removed. I think it is now really needed.

epd.py lines 131, 132
mcp_sram.py lines 74,75,84,85,113,114
all need & 0xFF added.

I am ready to fix this, if it is truely a bug.