exit status question

[Curtis Doty]

Not exactly sure if this is a bug. But I don't understand why only the 
first time running ((i++)) returns an error exit status.

Here's my script:

#! /bin/bash
echo $BASH_VERSION ${BASH_VERSINFO[5]}
set -x
#set -e
i=0
((i++))
echo $?
((i++))
echo $?

And here's what the output looks like:

4.1.7(1)-release x86_64-redhat-linux-gnu
+ i=0
+ (( i++ ))
+ echo 1
1
+ (( i++ ))
+ echo 0
0

Is there something tricky going on here? Why exit 1 the first time, but 
then normally every successive time? As you can see, I cannot set -e 
because it will just exit the script. Uncommented it above and it does 
this:

4.1.7(1)-release x86_64-redhat-linux-gnu
+ set -e
+ i=0
+ (( i++ ))

Doh! That was not an error.

../C