Weird image interposition in forum messages after 2.0 upgrade

[Superbetty]

I've just upgraded my forum from SMF 1.1.18  to 2.0.12
Everything went (more or less) ok, except for one very strange issue: my forum messages and signatures are now randomly interposed by an image, always the same (a smiley).
In order to test the upgrate I made a local installation of the forum, so unfortunately I can't give you a link, anyway I uploaded a screenshot of a message, just to help you understand what's happening.

It's a problem that affects old messages and new messages in the same way.

What I have already done:
- checked the database to see if the image path has been stored in the messages text: no, all the messages in the database are clean;
- run repair_settings.php. nothing changed.
- switched the language from english, to italian (the forum language), to english again, to italian again. nothing changed.
- switched to my theme, then to default theme, then again to my theme. nothing changed.

Any ideas? 

[Shambles]

Check your smiley list. One of them could have a blank (space) as its trigger.

That, or some (part of) of the words in your post that have been 'corrupted' match the trigger for a smiley.

[Superbetty]

that was exactly the problem!
and now I'm ashamed I didn't understand such an easy problem by myself 
thanks!