Bash sessions on OS X El Capitan (10.11) let source prompt.sh fail

[TimRobinNet]

When having bash sessions enabled (system default) and trying to run source prompt.sh, the following problem arises in prompt.sh:5
After executing DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )", $DIR contains /Users/tim/oh-my-git Saving session... ...saving history...truncating history files... ...completed., which obviously messes with the rest of the program.

Disabling bash sessions (http://stackoverflow.com/questions/32418438/how-can-i-disable-bash-sessions-in-os-x-el-capitan) solves the issue, but it would be nice to have a solution that wouldn't require this.