Projector display question

[kevn]

Hi. I have a Sharp projector that does 720p and 1080i. I believe the native resolution is 720 and that the 1080i is displayed "in Intelligent Compression." When I watch a blu ray using my PS3 and an HDMI cable and set it to 1080i, my projector says 540p as the display. The PS3 says it's displaying 1080i. When I set it to display 720p, the projector and PS3 both say they're displaying 720p. Now, when I connect component cables to the projector, and set it to 1080i, the projector says it's displaying 1080i this time.

My question is, why does my projector say 540p when I connect it with HDMI and use 1080i, and is this particular display significantly better/worse than the 720p I can choose instead. Because I can't tell much of a difference. My projector is a Sharp DT-400 if anyone is interested.

Thanks.