Structural Alignment works differently for prt and pdb files

Scenario for pdb

1. Open data/samples/PDB/1CF7.PDB
2. Right click on 3D view, select "Structural Alignment->Align With..."
3. Click OK in Structural Alignment dialog. Check Task report [StructuralAlignmentTask]:

Status  Finished
Time    0h 00m 00.013s

Structural alignment finished on 1CF7 chains [1,2,3,4] model 1 (reference) vs 1CF7 chains [1,2,3,4] model 1
RMSD = 0
Transform = 1 0 0 0
            0 1 0 0
            0 0 1 0
            0 0 0 1

Scenario for prt

1. Open _common_data/mmdb/2ZNL.prt
2. Repeat the same steps
   Current state: Task report [StructuralAlignmentTask]

   Status  Finished
   Time    0h 00m 00.030s
   
   Structural alignment finished on 2ZNL chains [1,2] model 3 (reference) vs 2ZNL chains [1,2] model 3
   RMSD = nan
   Transform = nan nan nan nan
               nan nan nan nan
               nan nan nan nan
               0   0   0   nan
   

    

 Also, instead of a 3D model, a black screen becomes, which disappears after clicking "Structural Alignment->Reset"