Yes, I posted about the same thing basically Restart movie Button for Movies in RC1
...without the AnyDVD part, which gives you the added frustration of trying to get back to the movie info and movie library pages.
In the 7 Beta there was the option to "Restart" the movie. This was true for VideoTS files, but other video files did not have that option.
Then in the RC builds, the reverse was true. Since I posted about this originally I have discovered that within the native WMC movies menu, neither DVD discs nor VideoTS files from a hard drive have the option of "Restart" from the beginning if you stop them. Other video formats however do have that option no matter if they are played from the "Movies" library or the "Videos" library. Going to the "Title Menu" or the "Root Menu" to restart doesn't help either although you can get back to chapter 1.
What I have had to live with to this point in the RC builds is to get back to chapter 1, skip forward to chapter2, then skip backward to chapter 1 (What a PITA). This also means that I have to let the movie play out through the credits at the end in order to have a new start the next time it is played. I am still trying to come up with a solution myself.
I am sorry that to this point I can really only confirm and commiserate with you on this. I know it is possible somehow to get this feature back, as it did work properly in the Beta. I have gone hunting through the registry a few times to no avail... I am hoping some of the more advanced members here will come up with something if MS doesn't "fix" it in the final.