P?TRTRS returns misleading info for non-square blocking factors

[Sideboard]

While solving a linear least squares problem of a skinny matrix using PDGEQRF, PDORMQR, and PDTRTRS, the latter returned info = -904, which denotes that the 4th entry of the 9th argument had an illegal value.

Excerpts from pdtrtrs.f:

!        1     2      3     4  5     6  7   8   9      10 11  12  13     14
PDTRTRS( UPLO, TRANS, DIAG, N, NRHS, A, IA, JA, DESCA, B, IB, JB, DESCB, INFO )

      PARAMETER          ( BLOCK_CYCLIC_2D = 1, DLEN_ = 9, DTYPE_ = 1,
     $                     CTXT_ = 2, M_ = 3, N_ = 4, MB_ = 5, NB_ = 6,
     $                     RSRC_ = 7, CSRC_ = 8, LLD_ = 9 )

*  M_A    (global) DESCA( M_ )    The number of rows in the global
*                                 array A.
*  N_A    (global) DESCA( N_ )    The number of columns in the global
*                                 array A.
*  MB_A   (global) DESCA( MB_ )   The blocking factor used to distribute
*                                 the rows of the array.
*  NB_A   (global) DESCA( NB_ )   The blocking factor used to distribute
*                                 the columns of the array.

But the check for this error involves the 5th (MB_) and 6th (NB_) entry of the the 9th (DESCA) argument instead of the 4th (N_).

            ELSE IF( DESCA( MB_ ).NE.DESCA( NB_ ) ) THEN
               INFO = -904

• Is this on purpose?
• Why do the blocking factors for rows and columns have to be equal? Is this documented?