powerline and iTerm2 shell integration no longer working together

XREF: powerline issue

• iTerm2: Build 3.1.4.beta.1
• OS: OS X Sierra (10.12.6)
• powerline: 2.6

When using powerline together with shell integration, the very first prompt of a shell works (iterm's little chevron is present and the first command gets recorded in Toolbelt > Command History), but all subsequent prompts do not call the iterm shell integration functions.

Commenting out powerline initializer results in iterm shell integration working as expected.

The behaviour is the same regardless of who is given first crack at PS1 (ie, if I move the iterm shell integration initializer below powerline's).

Contents of bash_login:

# iterm shell integration
test -e ${HOME}/.iterm2_shell_integration.bash && source ${HOME}/.iterm2_shell_integration.bash

# powerline prompt
powerline-daemon -q
POWERLINE_BASH_CONTINUATION=1
POWERLINE_BASH_SELECT=1
. /usr/local/lib/python2.7/site-packages/powerline/bindings/bash/powerline.sh

Contents of $PROMPT_COMMAND:

__bp_precmd_invoke_cmd; _powerline_set_prompt; __bp_interactive_mode

Unfortunately, I'm not sure how long the issue has been present, as I'm not a heavy user of Toolbelt Command History or navigating between prompts, and all the other shell integration features that don't rely on PS1 still work.

com.googlecode.iterm2.plist