Applying a paragraph style causes text to appear duplicated on screen, but it's not really.
CC 2018, OS High Sierra, both most current, brand new install on a brand new iMac Pro.
If I apply a style using a key command, 90% of the time the text from the cursor down goes crazy, looks duplicated. But if I hit the key command again, or click off the paragraph, or scroll, it goes away and is normal. So it's not really duplicating anything as far as I can tell. I screen captured exactly what it looks like.
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Richard Aguirre commented
I have frequently noticed this issue as well, particularly with long strings of text. It happens when applying a paragraph style that has space above built in, causing the lines below to bump down. Hitting escape or clicking out of the textbox clears the display glitch but this does slow me down since I can't apply multiple paragraph styles in a row if I can't see where they really are.