Undo boundaries inside macros?

[Robert Pluim]

<f3> 1 2 <f4> <f4> C-/ ; this undoes all the effects of the macro

<f3> 1 RET 2 <f4> <f4> C-/ ; this only undoes the '2'

I was expecting undo to be an all-or-nothing affair, but adding lines
introduces an undo boundary inside the macro. It matches what happens
when you type '1 RET 2' interactively, but should it?

Robert