Why round corners when I use marquee tool?

I use Photoshop 7.0, but hope someone can help me even though it's old.

I use the marquee tool frequently. It always used to have straight corners, but the past week it has started to automatically do round corners. I haven't changed any settings. Why does this happen?

I can mention that I use InDesign CS2. I have worked a lot with rectangles with round corners there recently, but every time changed the corners manually. After a couple of weeks though the program started to automatically change every rectangle to round corners. I didn't know how to change this, but after a couple of weeks it went back to straight corners automatically.

I use Windows Vista. Initially there was some problems to make it go with Photoshop and InDesign, but now it works fine most of the time.