Tested on Windows XP, 2.40 RC1, Radeon 9600. Also tried with 2.37a which failed to reproduce the error.

1. Use the included .blend file (a plain grid, the rightmost viewport is for showing the vertex that actually gets selected)

2. Go to edit mode (without moving the viewport) and try to select a vertex in the left viewport by right-clicking.
--> The result: the vertex outside the view gets selected.

3. Pan the view a bit so the whole grid shows.
--> Vertex selection works correctly.

4. Zoom in so that no border vertices are shown, try selecting vertices.
--> Vertex selection alternates between certain border vertices.

5. Pan the view so that the vertex in the upper right corner shows.
--> Vertex selection works correctly again.