[gembud] gdgrib error with two times in gdattim

I have a grid that contains a 3-hr precip value made by subtracting the 
previous 3-hr precip from the 6-hr precip, so it has two times.  When I try to 
write it out as a grib file using gdgrib, it always fails to find the grid, and 
mis-identifies the gdattim I asked for.


 GEMPAK-GDINFO>gdattim=f072:f069
 GEMPAK-GDINFO>r

 GRID FILE: 2015121706_gfshw.gem

 GRID NAVIGATION:
     PROJECTION:          CED
     ANGLES:                 0.0     0.0     0.0
     GRID SIZE:          720 361
     LL CORNER:             -90.00      0.00
     UR CORNER:              90.00     -0.50

 GRID ANALYSIS BLOCK:
     ANALYSIS TYPE:        BARNES
     DELTAN:               1.000
     DELTAX:           -9999.000
     DELTAY:           -9999.000
     GRID AREA:           -90.00 -180.00   90.00  180.00
     EXTEND AREA:         -90.00 -180.00   90.00  180.00
     DATA AREA:           -90.00 -180.00   90.00  180.00

 Number of grids in file:  1050

 Maximum number of grids in file:   5000

  NUM       TIME1              TIME2           LEVL1 LEVL2  VCORD PARM
  304     151217/0600F072   151217/0600F069        0         NONE C03M
 Parameters requested: GDFILE,LSTALL,OUTPUT,GDATTIM,GLEVEL,GVCORD,GFUNC.
 GEMPAK-GDINFO>ex
us-hou-intldm01:/data/gempak/model/gfs> gdgrib
 GDFILE    Grid file                         2015121706_gfshw.gem
 GFUNC     Scalar grid                       c03m
 GDATTIM   Grid date/time                    f072:f069
 GLEVEL    Grid level                        0
 GVCORD    Grid vertical coordinate          none
 GBTBLS    Input GRIB decoding tables
 GBFILE    GRIB data file name               /tmp/grib.grb
 VERCEN    PDS byte_4/byte_5/byte_6/byte_26
 PDSVAL    GRIB PDS grid identifier overrid
 PRECSN    Packing precision
 WMOHDR    WMO_ID/Origin_ID/DDHHMM
 CPYFIL    Grid file whose navigation is to  2015121612_gfshw.gem
 PROJ      Map projection/angles/margins|dr
 GRDAREA   Area covered by grid
 KXKY      Number of grid points in x;y
 Parameters requested: GDFILE,GFUNC,GDATTIM,GLEVEL,GVCORD,GBTBLS,GBFILE,
 VERCEN,PDSVAL,PRECSN,WMOHDR,CPYFIL,PROJ,GRDAREA,KXKY.
 GEMPAK-GDGRIB>cpyfil=2015121706_gfshw.gem
 GEMPAK-GDGRIB>r
Creating process: gplt for queue 1500938246
 [GR 4]  Invalid input for GPACK.  Defaults being used.
 [DG -7]  Input grid C03M ^151217/0600F07215 @0 %NONE cannot be found.