Maybe you are inadvertently recording to another audio track that has the record button lit - resulting in a 'phantom' recording.? That's caught me out once or twice.
Cubase 8.0.5 Build 418
System 1: AMD FX 8350 8 core 16Gb Win 7 64 Asus M5 A97
System 2: AMD FX 8320 8 core 16Gb Win7 64 Biostar A960D+
nb. Systems optimised using CoreParkingManager45. Windows 7 by default "parks" 4 cores on my systems and Cubase doesn't override this limitation - reduces peak performance. The problem is fixed I believe in Win8