When a MediaItem gets played, its metadata may change because the playback core is offering new metadata about this MediaItem that wasn't available when metadata was first read from it because it was added to a Library.
Following is a description of all cases where metadata may be overwritten automatically.
Title will be overwritten only if there is no value or if the value is equal to what it calculates the "default" value should be based on the url.
Because we set the "default" value upon insertion via the page scraper, or media import, we want to make sure to overwrite it if there's more complete metadata now available.
If you want to ensure that your metadata is always displayed, you will have to create alternate properties for your metadata and add columns for these properties. After doing so, you may hide the default columns so only your metadata is displayed.