There have been two bug fixes, one in TeX and one in Metafont. If you look into the tarball, you find a subdirectory called
errata. In it you find
In the last file there's a resumé of the changes, in the first two you can find the actual corrections.1
The bug fix in TeX is related to the control sequence with empty name.
428. \endcsname\csname should be followed by space in print_cs, just as all
other multiletter control sequences are (found by Oleg Bulatov, 14 Sep 2008)
@x module 262
begin print_esc("csname"); print_esc("endcsname");
begin print_esc("csname"); print_esc("endcsname"); print_char(" ");
If one runs the (admittedly bizarre) TeX file
% define the empty control sequence
% define another macro
% show \baz
the output on the terminal is
while, with the bug fix, it will be
as it should. The result of
\show applied to the empty control sequence is always represented as
\csname\endcsname: the bug produces invalid output, as it can be clearly seen.
The bug fix in Metafont is related to a memory leak:
572. Memory leak in make_ellipse on symmetric pens that don't have
a point on the x-axis (Eberhard Mattes, 03 June 2008)
@x module 536
done1: link(p):=s; beta:=-y_coord(h);
done1: if (link(p)<>null) then free_node(link(p),knot_node_size);
Congratulations to Oleg Bulatov and Eberhard Mattes (the creator of emTeX, by the way) for having being awarded the check from DEK.
By the way, there is a bug in the bug list: in the first above reported line it should be
Is this worthy a check?
1 An article by Knuth in TUGboat was published after I wrote this answer.