Problem: When uploading files via WebDAV to an IIS 7 server, the modified times are changed to reflect the upload time. This occurs even if the "Set file's modified time after upload to preserve date/time" option is enabled in the WebDrive client. 

Solution: This behavior occurs because, by default, support for custom properties is not configured in the WebDAV settings. Webdrive uses a custom property that it modifies using the PROPPATCH method to allow the original modified date to be used. This issue can be verified within the WebDrive log by searching for "424 Failed Dependency" error message associated with a PROPPATCH command. The resolution is to configure custom properties in WebDAV on the IIS server according to the link below.