[GAP Forum] Bug in modular determinant

["Decanato Fac. Matemáticas"]

Dear GAP Forum,

I encountered the following problem when I tried to calculate the 
determinant of a matrix of integers modulo 27:

gap> a := ZmodnZObj(1,27)*[[21,4,11,1],[0,25,11,1],[0,2,15,1],[13,19,4,1]];
[ [ ZmodnZObj( 21, 27 ), ZmodnZObj( 4, 27 ), ZmodnZObj( 11, 27 ),
      ZmodnZObj( 1, 27 ) ],
  [ ZmodnZObj( 0, 27 ), ZmodnZObj( 25, 27 ), ZmodnZObj( 11, 27 ),
      ZmodnZObj( 1, 27 ) ],
  [ ZmodnZObj( 0, 27 ), ZmodnZObj( 2, 27 ), ZmodnZObj( 15, 27 ),
      ZmodnZObj( 1, 27 ) ],
  [ ZmodnZObj( 13, 27 ), ZmodnZObj( 19, 27 ), ZmodnZObj( 4, 27 ),
      ZmodnZObj( 1, 27 ) ] ]
gap> Determinant(a);
Error, no method found! For debugging hints type ?Recovery from 
NoMethodFound
Error, no 2nd choice method found for `MultRowVector' on 2 arguments 
called fr\
om
MultRowVector( row2, Inverse( det ) ); called from
DeterminantMatDestructive( MutableCopyMat( mat ) ) called from
<function>( <arguments> ) called from read-eval-loop
Entering break read-eval-print loop ...
you can 'quit;' to quit to outer loop, or
you can 'return;' to continue
brk>

Ángel