So, if you right click on the timeline image and choose Speed/Duration, can you then change the length?
Really a one frame image that cannot be stretch has got to be something that’s viewed as footage. I have an AJA card as well and I just imported a Targa image with no trouble. Did you try resetting your preferences?
Until someone finds a solution, you could to put all these images in one folder, and do a batch save to PSD in Photoshop.
Good luck,
Vince