Okay, we're a tad further.
Today I have started from scratch again, with the full backup of my SMF 2.0.15 forum, then uninstalled all mods, made sure that the log was (and stayed) error-free and then performed the upgrade again.
Smileys were there.
Then I installed the shoutbox mod.
Smileys were gone.
Then I uninstalled the shoutbox mod.
Smileys were there, but I got errors about missing hooks.
Removed the hooks, smileys were there, errors gone.
Installed shoutbox, smileys were gone.
Left the shoutbox installed but deactivated in settings: Smileys were there, no errors.
Activated shoutbox again: Smileys are gone.
And indeed there are JS errors, two of them.
First error:
Error parsing header X-XSS-Protection: 1, 1; mode=block: expected semicolon at character position 1. The default protections will be applied.
index.php?action=post;topic=60554.0;last_msg=666330:1
Clicking on the error link shows that it complains about the main source's doctype, this "error" cannot be taken serious apparently:
<!DOCTYPE html>
Second error:
colorpicker.js:78 Error parsing header X-XSS-Protection: 1, 1; mode=block: expected semicolon at character position 1. The default protections will be applied.
ColorPicker_ColorBox @ colorpicker.js:78
The complaint concerns this line of code:
document.write('<div>');
and it complains about anything past the dot after "document".
This seems odd to me.
"document.write" should not be allowed anymore?
Cheers!
Mike