[CentOS] CentOS6 davfs2 shows invalid free/total storage capacity

Hello,

I have a CentOS6 VM with davfs2 where I mount WebDAV Shares;
one I have at a storage hoster and one I configured myself on a virtual 
server I rented on a hoster;
why does 'df' always show the same value for capacity

[root at centos6-vm ~]# df
Filesystem           1K-blocks     Used Available Use% Mounted on
/dev/sda3             11249272  7074512   3596664  67% /
tmpfs                   393264        0    393264   0% /dev/shm
/dev/sda1               218039    79340    127231  39% /boot
https://webdav.hidrive.strato.com/
                       26666664 13333332  13333332  50% /mnt/hidrive
https://myserver.example.com/webdav/
                       26666664 13333332  13333332  50% /mnt/webdav

the capacity of the hidrive is 5 GB and of mine abount 10 GB ...
several time ago I had a hoster, where the correct values where shown,
so this seems that this is a server setting, but how/where,
I'm just doing this on my server (CentOS with default Apache RPM):

DavLockDB /var/lib/dav/DavLock

Alias /webdav/ "/var/www/webdav/"

<Directory "/var/www/webdav/">
         AllowOverride None
         Options +Indexes
         Dav On
</Directory>

<Location "/webdav/">
         AuthType Basic
         AuthName "WebDAV"
         AuthUserFile /var/www/passwrds
         Require User walter
</Location>

are there any settings I can do on server side or can I do something on 
client side,
be shown correct values ...

Thanks,
Walter