Delphi: why breakpoints from time to time are not usable (green highlighted line on IDE)?

Question

From time to time I lose breakpoint functionality in Delphi.

I thought this to be a Delphi 2009 issue but now I have also it in Delphi XE.

In Delphi 2009 by

Answer 1

By using F9 to run the app, breakpoints will work as expected. I am using XE4 and I do not know if this will "fix" prior versions of Delphi.