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

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 deleting .dproj file I made the breakpoints work again.

In Delphi XE I am not able to make breakopints appear. I have update 1 with all hotfixes applied.

Does anyone have a solution?