Blurry playback, but sharp when drag clip itself alon timlin

Hello,
i'm new with Davinci and i noticed some strange thing. When i play clip hiting the spacebar or drag the cursor with mouse manualy along the clip the picture is blurry. But when instead i drag clip itself along timeline it's absolutelly sharp and clear. It's the same on 15.1 and 15.2.2.007 version. Are there any ideas?
Thanks.
i'm new with Davinci and i noticed some strange thing. When i play clip hiting the spacebar or drag the cursor with mouse manualy along the clip the picture is blurry. But when instead i drag clip itself along timeline it's absolutelly sharp and clear. It's the same on 15.1 and 15.2.2.007 version. Are there any ideas?
Thanks.