As you've pointed out, it looks as though this bug has existed for nearly a decade, but no one before you has reported it. Big thank you!
A simple fix for this is -
IN templates/default/post_side.tpl
AND templates/default/post_top.tpl
FIND TOWARDS THE BOTTOM:
{if $smarty.section.post.iteration == 1}{$island_insert}{/if}REPLACE WITH
{if $smarty.section.post.iteration == 1 && $post_layout != "gallery"}{$island_insert}{/if}NOTES:
The problem is that the special template for the gallery forums has its own $island_insert line which places the island right after the topic post. Then the gallery forum continues to generate replies using your forums default post layout. There isnt a need to call the $island_insert once again for gallery forums.
If the $island_insert is removed from the gallery post, then the $island_insert would not appear after the OP, but instead after first REPLY, which is not something we want.
This simple check should correct that.
