This also happens to me some time. I don't know the solution but here's workaround that works for me:
i'm not adding stops in RS code and I'm not using RS Engineer "Debug..." context menu options. I just attach debugger(Visual studio) to RsEngineer.exe and from it's leve I'm using Debug->New Breakpoint -> Function breakpoint and typing the name I need to stop on. (i.e for property formula it's Formula_MyPropertyName).