panel directory history

[/dev/rob0 <rob0 gmx co uk>]

It seems different in 4.6.1. In previous versions I knew what M-y and 
M-u would do, which is why I use them so much. But now in 4.6.1 I am 
not getting what I expect.

What I mean:
Start out in ~, hit Enter on directory 1/
Now you're in ~/1, hit Enter on directory 2/
Now you're in ~/1/2, hit M-y to go back
Now you're in ~/1, hit Enter on directory 3/
Now you're in ~/1/3, hit M-y to go back
Now you're in ~/1/2

Under previous versions you would have been in ~/1. M-y would take you 
to the directory you were last in. M-u would then bring you back. What 
happened?
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