I've been trying to figure out how I enabled this on my own, but haven't found a solution yet.
http://i.imgur.com/JrLyJlx.png
Right click in region capture and select "Region: Rectangle".

Thank you so much.
Thanks!
Is this accidental region mode changes happening using mouse wheel right?
I'm planning to swap it with ctrl + mouse wheel so that way instead it will just resize magnifier.
I feel like it was most likely me accidentally using my mouse wheel, because I had not messed with it using right click in the past at all before this happened to me.
[solved]
Maybe im a lame, or some issue with the traduction of myGUI,. but i cant find:
Right click in region capture and select "Region: Rectangle".
--> this 馃檲
And that oval wont go.
YAAAAY. After enabling the hotkey tooltips I found that the NUM 0 changes the shape, after I performing the hotkeys for "rectangle" capture!
Problem solved!
BY THE WAY, I love this product, I think I will be your patron.
Normally you select it from toolbar:

and if it is rounded rectangle then:

Most helpful comment
Right click in region capture and select "Region: Rectangle".