Watch out if you have a plugin like Joomlart's ja_thumbnail, that resets the $params variable, as it is passed by reference.
At least it will have to be adapted to detect that the content comes from K2 and return without touching anything, or as a root solution modify it so it only reads the parameters but not destroys them.
In the particular case of ja_thumbnail, you can add this code as the first line after the function onPrepareContent of ja_thumbnail.php plugin:
if (strpos($article->link, 'option=com_k2')) return;
This will make the plugin to do nothing if under k2.
A more elaborated solution would be to just do whatever it needs to do, but without re-assigning the parameters.
Best regards,
Willie