I've tried the process multiple times, and the result has always been the same. I created a 1.0-GB image, then mounted and formatted it using NTFS with compression. Then I created a basic volume RAM disk for that image.
What happens is that whenever I have compression Windows thinks the volume is out of space when it is not. For example, I can plainly see that only 600 MB is being taken up by files, but there is still no free space. The remaining space is not being taken up by $Recycle.Bin or by System Volume Information when this happens.
Simply disabling NTFS compression resolves the issue.
I saw this behaviour even on a regular hard-drive like C:\ when NTFS compression was on. It seems to happen when you create a bunch of small files, which in turn creates a large number of records in MFT and associated metadata.
Launching defrag R: /A /V where R: is the drive letter may shed light on where the space has gone.
Now I'm using a 2-GB RAM disk. I just got a notification from Windows that it was out of space. Disk properties and explorer told me there was no space left. Defrag.exe told me it was about 50/50 used/free space. So I ran compact.exe /u and by disabling NTFS compression, regained 817 MB.
There are only about 50 files on the entire disk. This makes no sense.