Breakpoints not visible sometimes in Disassembly window...

Hi,

  Environment: VS2010  and .NET 4.0

    We have implemented custom  Debug engine and necessary interfaces (IDebugPendingBreakpoint , IDebugBoundBreakpoint, IDebugDisassemblystream,...). Everything works fine. But sometimes if I create break point in normal editor window, breakpoints got disappeared in the disassembly window. And  when I click the break point location in the disassembly window, it correctly calls the remove break point implementation code (the only problem is breakpoints are invisible in disassembly window).

What could be the cause of the issue?

Thanks in advance,

Hari Prasad,M