Why TGRID recognized triangular faces as mixed?
 

When I read triangular boundary mesh into TGRID, which created in GAMBIT (all boundary faces were meshed with triangular cells), TGRID recognized it as mixed faces, not triangular ones. This resulted in such a thing: when I created several layers Prism cells in one wall, the prism cells overlapped with the connective boundary faces already meshed before, not remeshed the connective boundaries into tri and qua two parts automatically. So the interior cells generation failed. How to solve this problem? 3X.