非常奇怪的eclipse键盘行为/bug?

I am using Helios on Mac Snow Leopard. I don't know why but all of a sudden my arrow keys and delete button start not working only on Eclipse(so Eclipse ignores them) but the rest of the buttons works just fine. There is no exception/error thrown anywhere on the screen. I don't exactly know how to reproduce this malfunctioning. I am using Helios on Mac Snow Leopard. I don't