How to reproduce the bug:

File|New Project|Samples|Servlet Stateless (Java EE6)|Finish

In Projects window, project ServletStateless|Right click|Properties|Run
Change from "GlassFish Server 3" to "GlassFish Server 3 1"|OK

- Projects Window|Right click on project|Properties
- Run|Deploy on Save: uncheck it

In StatelessSessionBean.java,
Set a breakpoint on this line:

return "Hello, " + name + "!\n";

In Services Window|Servers|GlassFish Server 3 1|Right click|Stop
- Projects Window|Right click on project|Clean and build
- Projects Window|Right click on project|Debug
LineBreakpoint StatelessSessionBean.java : 39 successfully submitted.

Debugging works.

Insert code above breakpoint as follows:
    public String sayHello(String name) {
        if(name != null){
            throw new Error();
        }
        return "Hello, " + name + "!\n";
    }

and set breakpoints on new code.

Not able to submit breakpoint LineBreakpoint StatelessSessionBean.java : 39, reason: No executable location available at line 38 in class servlet.stateless.StatelessSessionBean.
Invalid LineBreakpoint StatelessSessionBean.java : 39

- Projects Window|Right click on project|Clean and build

Breakpoint is still broken.
- Projects Window|Right click on project|Debug
Breakpoint is still broken.
Debugger does not stop on broken breakpoint
- Try to set and unset breakpoint
Not able to submit breakpoint LineBreakpoint StatelessSessionBean.java : 39, reason: No executable location available at line 38 in class servlet.stateless.StatelessSessionBean.
Invalid LineBreakpoint StatelessSessionBean.java : 39

...

In practice, with my project, whenever I am in trouble and I make some code changes to see what is happening, then I am distracted by this failure, so NetBeans breaks when I need it the most.