Old .png files were used, not the new .svg ones
<thead>
<tr class="tableHead">
<th class="columnMark"><p class="emptyHead"><label><input type="checkbox" name="userMarkAll" /></label></p></th>
- <th class="columnUserID{if $sortField == 'userID'} active{/if}" colspan="2"><p><a href="index.php?page=UserList&searchID={@$searchID}&action={@$encodedAction}&pageNo={@$pageNo}&sortField=userID&sortOrder={if $sortField == 'userID' && $sortOrder == 'ASC'}DESC{else}ASC{/if}{@SID_ARG_2ND}">{lang}wcf.user.userID{/lang}{if $sortField == 'userID'} <img src="{@RELATIVE_WCF_DIR}icon/sort{@$sortOrder}S.png" alt="" />{/if}</a></p></th>
+ <th class="columnUserID{if $sortField == 'userID'} active{/if}" colspan="2"><p><a href="index.php?page=UserList&searchID={@$searchID}&action={@$encodedAction}&pageNo={@$pageNo}&sortField=userID&sortOrder={if $sortField == 'userID' && $sortOrder == 'ASC'}DESC{else}ASC{/if}{@SID_ARG_2ND}">{lang}wcf.user.userID{/lang}{if $sortField == 'userID'} <img src="{@RELATIVE_WCF_DIR}icon/sort{@$sortOrder}.svg" alt="" />{/if}</a></p></th>
<th class="columnUsername{if $sortField == 'username'} active{/if}"><p><a href="index.php?page=UserList&searchID={@$searchID}&action={@$encodedAction}&pageNo={@$pageNo}&sortField=username&sortOrder={if $sortField == 'username' && $sortOrder == 'ASC'}DESC{else}ASC{/if}{@SID_ARG_2ND}">{lang}wcf.user.username{/lang}{if $sortField == 'username'} <img src="{@RELATIVE_WCF_DIR}icon/sort{@$sortOrder}.svg" alt="" />{/if}</a></dipv></th>
{foreach from=$columnHeads key=column item=columnLanguageVariable}