Calling window.open opens the window, but then it flattens out

I make a call window.open

that opens the url I want, but then the window suddenly gets minimized without my interaction.

Why is this?

Update: The window was opened in an event onclick

(asp.net) then I pasted HTML. The linkbutton control was used, now when I converted it to asp:button

, it doesn't minify. Could you explain this?