Ubuntu – How to turn off mouse block selection in IntelliJ

For some reason, dragging the mouse cursor started doing block selects instead of the normal line select mode:

(Please ignore the fact that this image is from Visual Studio and not IntelliJ)

I tried pressing scroll-lock, pressing and releasing the alt/ctrl/shift keys, but still selecting doesn't revert to the normal "select full lines" mode. When I click and hold, then drag the mouse, I get a block (rectangle) selection.

Do you know how to undo this?

P.S. I'm running IntelliJ 9 on Ubuntu.

P.S. Holding SHIFT and pressing the up arrow button also does block select instead of normal multiline select.