Hi again
If I install more than one theme the icons expand/fold thread and show preview in the list of threads disappears on all themes except on the one marked as default in forum settings.

If you creates New topic or reply to a post and click on refresh all the buttons and icons on the right side crashes

You can see for yourself on this forum by change the theme to "standard" or "web 2.0", click refresh and the icons disappear. When the setting is the forum default ("Default (default)" in your case) it works normal.

Tested in IE8, IE10, IE11, Google Chrome on PC and standard browser and Boat Browser for Tablet on Android.

Best regards
Micke
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