I get the same problem, I also had similar experience with my HTC One, I've found out if I lock the screen after dialing number/contact it helps, a bodge job I know but stops me going through the menus with my ear lol!
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HTC One M8, Gunmetal Grey
Nexus 7 (2013)
Samsung Note 3, Sony Xperia Z1, HTC One, Sony Xperia Z White, Samsung Galaxy Note 2 Grey (N7100), Samsung Galaxy S3 Blue (i9300), HTC One X White, HTC Desire HD, Nokia Lumia 800, Samsung Galaxy S2 (i9200), iPhone 4, iPhone 3GS, iPhone 3G.