I've been chasing exactly this issue for weeks!! The problem I'm seeing is that something changes the binary/BCD flag. It turns out that changing this flag does

I've been chasing exactly this issue for weeks!! The problem I'm seeing is that something changes the binary/BCD flag. It turns out that changing this flag doesn't convert the current representation of time inside the RTC; it just changes the logic used to advance the counter fields and apply the next tick. So if you change that flag without also setting the time, then many of the fields are now invalid. But the tick logic doesn't care. It just sets the invalid fields back to zero and keeps on ticking. The year 20 17 becomes 1 4 1 1. The RTC clock is a 1984 part that is still getting embedded, more or less unchanged, into today's PCs. It is maddening.