Weird exit caused in a trap DEBUG which sources a file.

["Rocky Bernstein" <rocky.bernstein@xxxxxxxxx>]

Below is a small program whittled down from a larger one. It has
behavior I can't figure out.

It seems to show that when a function is called via trap DEBUG and you
then source a file and it has a statement in it, on return from the
TRAP an exit will be taken.  Here is the program:

#!/usr/bin/zsh
function debug_trap_handler {
    print $functrace[1]
    do_bug
}

function do_bug {
   . ./bug-file
}

trap 'echo EXIT hit' EXIT
trap 'debug_trap_handler' DEBUG
a=1
b=2
d=3

In "bug-file" put any command. ":" will do. Or a print statement.
Let's say it contains the line:
print bug file here

When I run the above I get:

$ ./zshtrace.sh

./zshtrace.sh:12
bug file here
EXIT hit

Now if the file contains only comments or blank lines or is empty,
here is what I get:
$ ./zshtrace.sh
./zshtrace.sh:12
./zshtrace.sh:13
./zshtrace.sh:14
./zshtrace.sh:15
EXIT hit

which is what I would expect.

Anyone care to venture a guess as to what's going on? It feels like a
bug to me, if for no other reason than some message about why the exit
was raised is missing.

Thanks.