You can use below different parameters depends on your requirements. To view documentation press ctrl+h in forms builder, use search feature to locate the topic.
'_self' Causes the document to load into the same frame or window as the source document.
'_parent' Causes the target document to load into the parent window or frameset containing the hypertext reference. If the reference is in a window or top-level frame, it is equivalent to the target _self.
'_top' Causes the document to load into the window containing the hypertext link, replacing any frames currently displayed in the window.
'_blank' (default) Causes the document to load into a new, unnamed top-level window. Note that these targets are lowercase and enclosed in single quotation marks.
hope this help you.
The target parameter is the very same as used in the target attribute of the a tag in HTML:
so what you did unintentionally was to open a link in a window called _blank; . This should be fine; however I'd give it a real name instaed.