That was a known bug introduced in one of the patches to Cubase Artist 6.5. Whichever version you have now, update it to 1 version higher and it should be fixed.
The problem also disappears if you disable the infoline, as it's related to that.
Software: Steinberg Cubase Artist 6.5.5 64-bit.
Hardware: HP elitebook 8530b with W7 Home 64-bit
Mackie Onyx 1620i - Steinberg Midex 8 - Steinberg CC121.
Analog: Alesis M1 - Behringer Powerplay Pro-XL - Studio Projects C3 - AKG K612Pro
Instruments: Yamaha DTX750k - Yamaha MO-6 - Yamaha CP5 - Waldorf Blofeld - Korg Wavedrum WDX.
Plugins: Native Instruments Prism - Rob Papen Distort - Rob Papen Delay - Halion Symphonic OrchestraMy humble contributions to what could be considered music.