Alpha_11, SP3, media items set to 'marquee select items and time'
If the checkbox for 'move edit cursor when starting marquee selection' is unchecked, then clicking on media items is sketchy, usually not moving the edit cursor, or moving it unpredictably.
Also, this shouldn't be the default setting checked, not many users will want this I assure you. You might be thinking of time selection+marquee, which should be default imo.