My work is looking at using Microsoft's DPM as a backup solution.
We have set up a test environment that includes a DPM 2007 (service pack 1) server protecting a SQL 2005 (service pack 2).

I found that DPM was a little troublesome to install, but once it was running the UI is intuitive and functional.
But as I was putting it through it's test paces I ran into an issue that I can not find a definitive answer for in the official documents or otherwise.

As I was selecting restore points I noticed that once I had used a restore point that I could no longer select that point nor any point prior.
For instance, I had DPM installed on May 11th.
In testing I restored to a state recorded on May 27th at 22:00.
Now I have lost the ability to restore to any time prior to May 27th at 22:15.

It seems that DPM only backs up using a snapshot and once that snapshot is implemented it is lost.

But I am only using a short-term back up solution to disk (we don't have tapes available for testing). I was wondering if I used the long-term solution if I would encounter the same issue -that is, if I restore to June 1st from tape do I lose the ability to restore to any point prior?

Is that just the way DPM operates regardless of whether your back up plan is long-term or short-term?