After the breakpoint is set, a new line breakpoint marker appears in the prefix area of the editor and in the Breakpoints view. This marker appears as a filled dot. When the debug session for the program begins, the breakpoint appears in the Breakpoints view and in the editor with a check mark overlay. When the debug session terminates, the breakpoint becomes a filled dot again. The overlay check mark, which indicates that a breakpoint is installed in a debug session, is gone. The next time that a debug session is launched for the program, the breakpoint will be installed again (with a check mark overlay in the Breakpoints view and in the prefix area of the editor). The breakpoint will be removed only if you delete the marker or the resource file that contains the marker.
When you have multiple debug sessions active and you open source in the editor and set a breakpoint in it, a breakpoint request is sent to all of the debug sessions. If any debug session can set the breakpoint, a check mark will overlay the filled dot for this breakpoint in the Breakpoints view and editor to indicate that this breakpoint has been installed. If none of the debugging sessions can set the breakpoint, it will remain in the editor and in the Breakpoints view as a filled dot, and it will not have a check mark overlay.