To prevent this making COBSQL hang, use the COBSQL directive SQLDEBUG. Then, when COBSQL encounters such a line, it displays:
CSQL-W-040: Pro*Cobol commented out the following line
The program logic is altered because Pro*Cobol has commented out a COBOL line. We recommend, therefore, that you do not execute programs that produce this message. You should either remove the comment text or terminate the Embedded SQL statement with a period.