When creating a tcz with mksquashfs you should make sure that you delete any existing package with the same name in the directory where you create the new one. In case not mksquashfs will append your new data to the existing archive, but it will place it under a different path, e.g. things to be put under /usr will be placed under /usr_1 etc. This means that the archive will contain both the old and the new data, the size of the archive will not be doubled since must of the data in the two trees are identical and the compression takes care of representing identical data just once. However since the newest data will be located under /usr_1 this is not the data that will be available once the package is installed, but the oldest tree in the archive (the /usr tree) will be the data used in the running system.
I noticed this on the most recently submitted qt-4 packages, so they ought to be rebuilt.
Kind Regards
Lars