bug#12985: eval-last-sexp looks broken when executed twice

[Kelly Dean]

Using 24.2, type:
5
Then do C-x C-e, and as expected it echoes:
5
But then do C-x C-e again, and unexpectedly it echoes:
5 (#o5, #x5, ?\C-e)
The same thing happens if you type 5 then do C-u C-x C-e C-u C-x C-e; first as 
expected you get:
55
Then unexpectedly you get:
5555 (#o67, #x37, ?7)