This is a bug I've noticed since Studio 2009.
If you select multiple segments by dragging the mouse down (say, from segment 32 down to 39) and then press Ctrl+Enter, it confirms all the segments from 32 to 39. However, if you do the same operation by dragging the mouse UP (say, from segment 55 up to 49) and then press Ctrl+Enter, it confirms *all the segments in the file*. This can be quite vexing when you have just started a new file with 5000 segments and suddenly they are all confirmed.