tetex bug, array environment

I think this is a bug. If it's in Tex itself
Donald K. owes someone a dollar. :-)

-burt


=====================================

\documentclass[11pt]{article}
\begin{document}

\[
f(x) = \left \{
       \begin{array}{lll}
      [4,5] & x\in [0,2) & \\
% BEGIN SECTION OF INTEREST
% bug
%
        [0,1] \cup [4,5] & x\in[2,3] & \\
        [0,1] &  x \in (3,5] & \\
%
% error reads:
%! Illegal unit of measure (pt inserted).
%<to be read again> 
%                   >
%l.14         [0,1]
%                   \cup [4,5] & x\in[2,3] & \\
%
% bug workaround
%    {}  [0,1] \cup [4,5] & x\in[2,3] & \\
%    {}  [0,1] &  x \in (3,5] & \\
%
% END SECTION OF INTEREST
       \end{array}
       \right.
\]

\end{document} 

==============================================