Most likely this indicates a file permission problem on your installation.

The /Data folder must be writable by the web process. We create cache dependency files that are used to clear the cache but if it can't write to those files then the only way the cache gets cleared is by touching the Web.config.

If you moved the installation from one machine to another you may have some funky permissions on existing cache dependency files. In that case try deleting them and they should be re-created automatically if file permission on the folder are correct. The files you want to delete are all files in the folder /Data/Sites/[SiteID]/systemfiles where SiteID will typically be 1 in a single site installation.

Hope it helps,

Joe