What file format are you using? Some formats don't store resolution values, so they'll come in at the default 72 dpi. But the pixel count will remain the same.
File format from the image is saved as a .jpeg. Format into the new project is started as a custom project then saved as a .jpeg and as a psd.
Photoshop stores resolution data in JPEG, and EXIF can store resolution data -- but some other applications don't store resolution information.
It sounds like you might be using another application. If so, which other application are you using?
And is Photoshop keeping the correct number of pixels and just losing the resolution?
I use LR3 to edit, then bridge over to PS5. Here's what I did, and it seems to have done the trick. I opened a new project, but rather than opening it as custom, I opened it as a photo, then made it into custom sizes. It worked on the projects that I was having trouble with and the PPI seems to be fine. Weird.
And yes, it is keeping the resolution, just cutting out the pixels.
I am totally stumped and consider myself fairly well versed in Photoshop.