echo "1" after shortcode on HHVM

Dear Developers,

I try using shortcode-exec-php on HHVM instead of php5.5.
but It used the environment, all shortcodes echo “1” after shortcode scripts.
It don’t occured by php5.5(without accelerators).

My environment is…
OS : Debian 3.2.60-1+deb7u1 x86_64 (wheezy 64bit)
HTTP Server : Nginx 1.6.0

The issue isnt high priority but I want use this plugins on HHVM.
I wonder if you check and fix it.

https://wordpress.org/plugins/shortcode-exec-php/