I've got these lovely 150MB scans (slide film is the coolest thing in the world). When I add a Curves adjustment layer (to compensate for my incompetent scannin' technique), the file size nearly doubles! What the hell's up with that? 150MB I could deal with. 300MB makes me awfully sad.

Google turned up this, so I know I'm not alone.
http://www.andrew-hall-artist.com/journal/index.php?p=107

Is something broken?