The Menu not popped up on clicking in dual screen setting

[ddreamer]

Hi, I am a newcomer for Linux Mint. What I installed is Linux Mint Debian Edition 201204 on a laptop with nVidia GeForce 9500M GS card. I have not changed the default desktop manager. I am not sure if the desktop manager is MATE. But it looked just not like cinnamon. If I put the question in the wrong place, please tell me.

The resolution of the laptop is 1440x900 while the other monitor which can be tuned to the highest resolution of 1920x1080 is connected to the laptop. "mate-display-properties" did a good job to configure the second screen to be rotated 90 degrees to be an extension left to the primary screen when the resolution of the second screen is set to 1440x900 (same as the primary screen).

When the second screen is tuned to the maximal resolution of 1920x1080, everything still looked fine. But the Menu button at the bottom left corner of the primary screen just did not respond to mouse clicking. When the resolution is set back to 1440x900, the problem resolved.

Thanks