Report of a new (I think) vi bug

[tektronix!zehntel!sytek!menlo70!hao!csu-cs!silver]

vi file1	(say, 100 lines)
50G		(go to a line in the file)
:$r file2	(read file2 at end; cursor now at first line of file2)
u		(undo; cursor back at line 50 and total buffer is back
		 to 100 lines, but lines 51-100 are the last 50 lines
		 of file2, not file1 !!!)