Clock Keeps Going Back One Hour (DST Still Checked)

As title says. I live in UTC/GMT, and DST is on. For the past few weeks now, the clock seems to go back one hour, as if reporting normal time, yet the daylight savings time option is still selected (and if I un-check it, it goes back two hours--one for the DST, and one from the going back by itself).

Why it does this, and it's actually f-ing with my schedules since I've been one hour late to a couple of things now due to this small but rather colossal error. I actually have to Google my time instead of looking at the bottom right corner, which is so ridiculous.