Not reproducable here. If you drag an entire disk onto RAM:, diskcopy will complain that the object is of wrong type and cannot be copied (which is true, RAM: is a handler without underlying device). If you drag the contents of a volume onto a disk, everything can be removed again. If you drag contents onto RAM: and RAM: gets full, you can either answer to remove the incomplete object, which it always does completely, or leave the incomplete object on disk. In this case, you may end up with a .info without a corresponding file or directory, but in any case, they could be deleted fine.
To clarify, I am opening up the RAM: disk to show its window on workbench. I then drag a disk icon into the window of the RAM: disk and do the copy (this is not a diskcopy). As you mentioned there are 2 ways to delete files in workbench after I get the "disk is full" prompt:
1) Cancel the operation and say no to "remove incomplete object" Then use the menu item to delete entire directory by selecting it within the RAM: window. This one deletes the directory and the *.info file.
2) Cancel the operation and say yes to "remove incomplete object" In this situation, the *.info file is left in the RAM: disk. Not a big deal as I can delete the *info if need to manually.