Looks like I'm unable to set site logo on the search result page through applying custom master page referencing a css. Looks like there is inline css on this page. Also the welcome content type using Search People page layout, it has the same issue. Here is my Design Manager SiteLogo snippet:
<div data-name="SiteLogo">
<!--CS: Start Site Logo Snippet-->
<!--SPM:<%@Register Tagprefix="SharePoint" Namespace="Microsoft.SharePoint.WebControls" Assembly="Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c"%>-->
<!--MS:<SharePoint:AjaxDelta runat="server" BlockElement="True">-->
<!--PS: Start of READ-ONLY PREVIEW (do not modify)--><!--PE: End of READ-ONLY PREVIEW-->
<!--MS:<SharePoint:SPSimpleSiteLink runat="server" CssClass="" ID="x4ceadb20ece54c0d8c023aed9db14508" NavigateUrl="~sitecollection">-->
<!--PS: Start of READ-ONLY PREVIEW (do not modify)--><!--PE: End of READ-ONLY PREVIEW-->
<!--MS:<SharePoint:SiteLogoImage name="onetidHeadbnnr0" runat="server" CssClass="" ID="x80aae98142e54113bd0e73cdb3cfccba" LogoImageUrl="/_catalogs/masterpage/mycompany/images/dentonsLogonew.jpg">-->
<!--PS: Start of READ-ONLY PREVIEW (do not modify)--><img id="ctl00_x80aae98142e54113bd0e73cdb3cfccba" name="onetidHeadbnnr0" Src="http://portal.mycompany.com/_catalogs/masterpage/mycompany/images/MyCompanyLogo.jpg" alt="My Company Intranet" /><!--PE: End of READ-ONLY PREVIEW-->
<!--ME:</SharePoint:SiteLogoImage>-->
<!--PS: Start of READ-ONLY PREVIEW (do not modify)--><!--PE: End of READ-ONLY PREVIEW-->
<!--ME:</SharePoint:SPSimpleSiteLink>-->
<!--PS: Start of READ-ONLY PREVIEW (do not modify)--><!--PE: End of READ-ONLY PREVIEW-->
<!--ME:</SharePoint:AjaxDelta>-->
<!--CE: End Site Logo Snippet-->
<!--CE: End Site Logo Snippet-->
</div>