Altitude MCP vs PMDG 737

Good morning everybody! I use OC MCP/EFIS together with my PMDG 737. Generally, everything works quit okay, but i have a strange effect with the altitude display on my MCP that appears only when flying using LNAV/VNAV: i select a new target altitude for the upcoming decent (e.g. 3.000 ft) after TOD and the aircraft begins to descent - so far so good, but during the descent, the altitude display on my MCP suddenly shows a value, that is not selected! The PFD shows 3.000 ft, but the OC MCP shows 1.600 ft - whereas the PMDG MCP shows 3.000 ft as well - does anybody know this effect and how to solve the problem?

Thx in advance, best regards, merry xmas and a happy new year to everybody!