I have a new observation which might serve you as a hint.
While processing, if I click on (make active) the Background Tasks tab (upper section of Audio Window), suddenly the remaining time value on the bottom (under wave) appears and decreases accordingly. If I click elsewhere (like on File Browser), remaining time value stays but freezes e.g. it does not decrease anymore. Clicking back on the Background Tasks the value refreshes again etc.
Win7 x64 SP1, Intel Core i7-2600K 3,4 GHz, 16 GB RAM, Gigabyte GA-P67A-UD4-B3, RME Fireface 400, MIDISport 4x4, ATI Radeon HD 5750 + 2x HP ZR2440w displays
Cubase 6.5.5 WaveLab 8.0.3, HALion 5