R – IE6 and IE7 send HTTP/1.1 without hostname on redirect

we use Redirect-after-Post Pattern in our webapp.

Sometimes very few error logs are shown in our apache log like this:

[error] […] client sent HTTP/1.1 request without hostname (see RFC2616 section 14.23): …

in my acces log they show up as
[…] "GET /xyz/ HTTP/1.1" 400 226 "-" "-" 72

What happens here is: The application sends a redirect with an absolut URL like this:

Location: http://www.kicktipp.de/demo/

Today i have three browsers which are requesting the URL to which we redirect without required Host header:

• "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; GTB6; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.5.30729; .NET CLR 3.0.30618)"
• "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 1.1.4322; .NET CLR 3.0.04506.648; InfoPath.1)
• "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Mozilla/4.0 (compatible; MSIE 7.0; Win32; WEB.DE); Mozilla/4.0 (compatible; MSIE 8.0; Win32; WEB.DE); .NET CLR 1.1.4322; InfoPath.1; .NET CLR 2.0.50727; OfficeLiveConnector.1.4; OfficeLivePatch.1.3; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)"

These were all normal visits, users clicked a few pages, then got a redirect and it fails with an error.

I know that some old browsers need help with http/1.1 so we have the default debian setenv configuration:

<IfModule mod_setenvif.c>

#
# The following directives modify normal HTTP response behavior to
# handle known problems with browser implementations.
#
BrowserMatch "Mozilla/2" nokeepalive
BrowserMatch "MSIE 4\.0b2;" nokeepalive downgrade-1.0 force-response-1.0
BrowserMatch "RealPlayer 4\.0" force-response-1.0
BrowserMatch "Java/1\.0" force-response-1.0
BrowserMatch "JDK/1\.0" force-response-1.0

#
# The following directive disables redirects on non-GET requests for
# a directory that does not include the trailing slash.  This fixes a 
# problem with Microsoft WebFolders which does not appropriately handle 
# redirects for folders with DAV methods.
# Same deal with Apple's DAV filesystem and Gnome VFS support for DAV.
#
BrowserMatch "Microsoft Data Access Internet Publishing Provider" redirect-carefully
BrowserMatch "MS FrontPage" redirect-carefully
BrowserMatch "^WebDrive" redirect-carefully
BrowserMatch "^WebDAVFS/1.[012]" redirect-carefully
BrowserMatch "^gnome-vfs/1.0" redirect-carefully
BrowserMatch "^XML Spy" redirect-carefully
BrowserMatch "^Dreamweaver-WebDAV-SCM1" redirect-carefully

</IfModule>

It occurs only once per 10000 redirects. but of course i want to satisfy every user and every browser.

Is there any hint you can give me? Do wee need to add even more browsers to our mod_setenvif configuration?