Is the call to Bar::DoBarInternalStuff the last statement in Bar::DoBarStuff? If so, the compiler most likely replaced Bar::DoBarStuff's stack frame with Bar::DoBarInternalStuff's when Bar::DoBarInternalStuff was called.
This kind of tail call optimization is fairly common in C/C++ compilers. It reduces the stack depth required when a recursive function can be arranged such that the recursive call is the last call in the function.