underscore in front of a goodie escapes symbols from beeing converted.

Do you have a few actual examples?

yes, here are some strings that worked on 0.10.4 but do not work on 0.11.2.1:

• _{*} hello{o} {OK}_{X}
• {*} {o} {X} are not rendered
• only {OK} is rendered on both configs.

If a + or - or , is used between two smiley-expressions it works, both are rendered correctly, but _ or characters between smiley-expressions prevent the second one from being rendered.

In fact I use the plugin in a modified version for my page, where I added some more expressions for images of key-stroke-icons like "SHIFT" or "CTRL" or "ArrowUP" to smileys.py. There it looks sometimes better to append such images immediately after some characters.

If all three smiley of {OK}_{OK}xxx{OK} would be rendered it would be great. In general, forcing a smiley to be rendered independent of the preceding character would be great. But of course not inside macros or special {{{ ... }}} sections, this can be used to prevent smileys to be rendered.

Only a single ! should escape a smiley from being rendered, double !! would be expected to be rendered as a single ! with immediately preceding smiley.