phpBB3 requires that smiles have a space preceding the smiley code whereas phpBB2 does not.
For instance, these work in phpBB2

:lol::lol::lol::lol:

and

(:lol:)

but in phpBB3 with the multiple inline smilies, only the first smiley code is parsed and the one with the brackets surrounding the smiley does not work at all.

The attached patch file will add the necessary spacing to allow these smilies to work in phpBB3.