Well, this is kind of gross.

The reason for this is as follows: first, to know the result of "make -q" make just needs to locate at least one target that will be rebuilt.  Once it finds the first target that will be rebuilt, then it knows the exit code should be "1".

So, you ask it to build "foo".  It sees that "foo" depends on "bar", so it determines whether "bar" will be rebuilt.  Here's where it gets tricky: make has special handling for recipe lines that contain "$(MAKE)", and those which start with "+"; if you run "make -q" (or "make -n" etc.) then these lines will actually be invoked anyway.  See the documentation section "How the 'MAKE' Variable Works".

The idea is that in a recursive make environment if we want to know if any target needs to be built we need to recursively invoke make to see if it will build anything.

So, make is recursively invoked (with -q set) and we discover yes, we need to build "baz", so the recursive invocation of make exits with a "1" exit code.

Unfortunately the parent make doesn't really understand that, and it just says "oh, my target failed!" and so it then decides to exit with an exit code of "2" because something failed.

Yuck.  I agree that this is probably a bug.  Make needs to understand that it's invoking a recursive make with -q mode enabled, and if it exits with a "1" then it should treat that as a "must make target" exit code and itself exit with a "1", not a "2".  I've checked and this wrong behavior has existed as far back as I have compiled versions of GNU make (3.74, released in 1995).

As for why it works if you put some other line before the recursive make: in that case before make runs the recursive line it sees that there is some other recipe line that must be invoked, which is not marked as a recursive make invocation (it doesn't contain "$(MAKE)" and it doesn't start with "+").  So, make immediately knows that this target will be updated and it can stop right away without doing any recursive make, and exit with "1".

You may be confused because you think you added a make comment line, but you didn't: remember that ANY line which is indented with a TAB character, REGARDLESS of what it contains, is considered a recipe line.  So that is not interpreted as a makefile comment, because it's indented with a TAB.  Instead it's going to be expanded and passed to the shell.  If you remove the TAB before the comment line, so it's considered a makefile comment, you'll get the "old" behavior (exiting with error 2).