Even I'm able to reproduce this issue on my mobile browser. Below are configuration details:-
Phone - HTC Desire S
OS - Android 2.3.5
Browser - Opera Mobile 14.0.1074.57453
When I tried to scroll the page right side then I noticed this space... In normal position screen is correct but when we try to scroll to see whether there is anything on right side or not then this black screen comes... It should not come .