Somehow, the feeling of context menu opened on the left side seems to be on the wrong side as it covered important information of the current application and therefore losing context of current action.
This is a Table PC Settings which assumes the user is holding a pen and needs to see the context menu without moving the hand compared to using a mouse has nothing blocking the view.
To change the setting:
1) Windows Run
2) shell:::{80F3F1D5-FECA-45F3-BC32-752C152E456E}
3) At Tablet PC Settings dialog, change to Other tab and change Handedness setting.