Different content delivered to Internet Explorer than to Chrome?

Question

We recently noticed some rendering issues in the Chrome browser for our SharePoint 2010 site. The differences are primarily the top nav/horizontal nav and the quicklaunch navigation.
Here's an example of our top nav code:
<asp:ContentPlaceHolder ID="PlaceHolderTopNavBar" runat="server">
<asp:ContentPlaceHolder ID="PlaceHolderHorizontalNav" runat="server">
<SharePoint:AspMenu ID="TopNavigationMenuV4" runat="server" EnableViewState="false"
DataSourceID="topSiteMap" AccessKey="<%$Resources:wss,navigation_accesskey%>"
StaticSubMenuIndent="0" StaticPopOutImageUrl="/_layouts/images/whitearrow.gif"
UseSimpleRendering="true" UseSeparateCSS="false" Orientation="Horizontal" StaticDisplayLevels="2"
MaximumDynamicDisplayLevels="2" SkipLinkText="" CssClass="s4-tn" />
<SharePoint:DelegateControl runat="server" ControlId="TopNavigationDataSource" ID="topNavigationDelegate">
<Template_Controls>
<asp:SiteMapDataSource ShowStartingNode="False" SiteMapProvider="SPNavigationProvider"
ID="topSiteMap" runat="server" StartingNodeUrl="sid:1002" />
</Template_Controls>
</SharePoint:DelegateControl>
</asp:ContentPlaceHolder>
</asp:ContentPlaceHolder>
The Chrome browser is actually receiving a different response than Internet Explorer from the server. Chrome receives this additional CSS code within a style element just before the end of the head element:
.zz1_TopNavigationMenuV4_0 {
background-color:white;
visibility:hidden;
display:none;
position:absolute;
left:0px;
top:0px;
.zz1_TopNavigationMenuV4_1 {
text-decoration:none;
.zz1_TopNavigationMenuV4_2 {
I checked this behavior by requesting the page using cURL using IE's user-agent string and using Chrome's user-agent string and found the same difference.
Additionally, the output HTML output of the menu is different. The Chrome version uses a series of span elements to contain just teh top-level links, whereas IE uses nested unordered list elements (ul) to display multiple levels of navigation.
Is it normal SharePoint behavior to delivered different content to different browsers? I should be able to override the Chrome-specific CSS by using more-specific selectors, but I'm curious if others have run into this issue, and if so, how they have addressed
it.

Answer 1

Update:
I already tested different user-agent strings, as I noted in my initial post.
I do have a modified compat.browser file (in C:\inetpub\wwwroot\wss\VirtualDirectories\[sitename]\App_browsers\compat.browser (isMobileDevice is set to false for iPhone and some other devices). This certainly seems like a likely source of problems, but
the same file, when applied to a development development environments, does not cause the same problem.
Production and development environments are all running Microsoft SharePoint Server 2010, database version 14.0.5136.5002.
I changed the custom masterpage to an OOB masterpage (nightandday.master). Although the top nav is not present in that masterpage, the differences between Internet Explorer and WebKit browsers were apparent. (The differences are not apparent in the development
environments).
Disabling the custom top nav feature does not address the issue (i.e. the default top nav exhibits the same problem)
Additionally, as suggested on some other sites, I checked the mozilla.browser file at C:\Windows\Microsoft.NET\Framework64\v2.0.50727\CONFIG\Browsers. The file contains an entry that should match Safari and Chrome, but is identical across the production
and development environments:
<browser id="Safari" parentID="Gecko">
<identification>
<userAgent match="AppleWebKit/(?'webversion'\d+)" />
</identification>
<capture>
</capture>
<capabilities>
<capability name="appleWebTechnologyVersion" value="${webversion}" />
<capability name="backgroundsounds" value="true" />
<capability name="browser" value="AppleMAC-Safari" />
<capability name="css1" value="true" />
<capability name="css2" value="true" />
<capability name="ecmascriptversion" value="0.0" />
<capability name="futureBrowser" value="Apple Safari" />
<capability name="screenBitDepth" value="24" />
<capability name="tables" value="true" />
<capability name="tagwriter" value="System.Web.UI.HtmlTextWriter" />
<capability name="type" value="Desktop" />
</capabilities>
<controlAdapters>
<adapter controlType="System.Web.UI.WebControls.Menu"
adapterType="System.Web.UI.WebControls.Adapters.MenuAdapter" />
</controlAdapters>
</browser>
I was finally able to reproduce the issue in a development environment when I changed removed the adapter element from compat.browser and restarted IIS:
<browser id="Safari2" parentID="Safari1Plus">
<controlAdapters>
<adapter controlType="System.Web.UI.WebControls.Menu"
adapterType="" />
</controlAdapters>
</browser>
The chain of browser property inheritance appears to be:
Default > Mozilla > Gecko > Safari > Safari1Plus > Safari2
The asp.net menu control not rending correctly in safari thread on Stackoverflow suggests a workaround, although since I
have development environments not exhibiting the behavior I feel there is another way to address the issue.