Photos are bright for a split second, then are dark in Lightroom

It seems that whenever I take a bunch of pictures, I preview them on the LCD screen for general brightness & sharpness & histogram as most do. They look pretty good as far as correct exposure.

Then I come home and import them to lightroom (latest version 2.1). The weird thing is, when I first scan/preview a photo full screen, the exposure looks the same as what I saw on the LCD for a split second, then it goes much much darker. I literally have to adjust the exposure slider to about .50 to get back to "normal" on nearly every photo... After it goes darker (I assume rendering the preview) I never see the "bright" version again.

I tried switching between all available camera profiles (have the final release ones) and it still stays dark.

Any ideas as to why it would do this? It's applying some default profile I suppose... But I guess I don't want it to, because adjust the exposure slider that much adds quite a bit of noise.

And I'm using a 50D, but I think I had the same issue with my XSi as well.

Thanks in advance for any ideas...

I'm not totally sure, but I think the initial "preview" shown in Lightroom is from the jpeg file that is embedded in the RAW file by the camera at the time of capture. Then, as Lightroom renders its own previews, these are displayed instead.

Are you using the new calibration profiles (included as a separate .dmg with ACR 5.2)? These really improved ACR's rendering for me.

On the import screen, do you have the box near the bottom checked telling Lightroom to aply some kind of treatment upon import?

Are all of your sliders in their detents once the pics are uploaded and (if you're using them) previews have finished rendering?

Sounds to me like LR is making its own adjustments that you don't want made. Especially if your histograms look ok on the camera while shooting.

I ran the Adobe updates last week that updated ACR 5.2 for my CS4 - which added the final calibration profiles to both ACR and LR... So yes, I'm using them.

On the import screen I have Development settings set to "none".

All of the sliders are at default -

White Balance - "As Shot"
Exposure - 0
Recovery - 0
Back Light - 0
Blacks - 5

Brightness - +50
Contrast - +25

Clarity - 0
Vibrance - 0
Saturation - 0

I was just checking them and they definitely appear "brighter" in DPP when opened with default settings... It might not need +.50 exposure in LR, but it seems like I adjust every photo +.20 - +.30...

Do you think maybe the +25 default contrast could make them look darker?

I'd just set the brightness higher, and save that as a new default.