Output buffering changed on display?

[machavity]

I was updating our internal development server to PHP 7 and found that Smarty 3.1.17 didn't play well with it, but 3.1.29 did. No problem, I updated. Afterwards, I noticed a problem with FirePHP saying that headers had been sent. I assumed it was a PHP7 issue but when it went to production it was doing the same thing so no redirects were working. After rolling it back I solved some of the problems by rolling my development up to the latest unreleased in the GitHub repo, but the problem with display() still remained.

After playing with it, I changed to echo $smarty->fetch(); and it works again.
I'm not sure what changed here but does anyone know what changed in display() to make it output headers? Even running ob_start wouldn't fix it

[uwetews]

I suspect that you have PHP files which do have some characters like newline after the ?> at file end.
These could cause the header send problems as for performance we did flush() the output buffers instead of echoing its content.
Better remove all ?> tags at files end as it is not needed.
However reverted the code to echo the output again on echo.

The fix is now in the master branch.