I was assuming that the images no longer had an alpha channel. What I was trying to say is that somehow Quark is still seeing and using the alpha channel from the previous image, so internally to quark it has become detached from the original image and embedded into the quark Document. There are 3 ways I could think of that you could exchange your original psd image to the EPS with a clipping path; 1 you can place the new file, scale and move into position and delete the old; 2 you can go to Picture Usage and update a missing or modified file (dangerous when swopping file type): 3 you can use the Script to update a picture maintaining scaling and position. I must apologise that it appears option 3 is no longer available and has been replaced by the Maintain Attributes checkbox inside the File>Import window, you could try and see if having this checkbox unchecked would clear the alpha channel data?
... there was the puzzle of why the sun came out during the day, instead of at night when the light would come in useful.