Field SQL_DESC_COUNT should fit into a variable of type SQLSMALLINT. But when retrieving this field of APD SQLGetDescField returns SQLINTEGER value. So memory corruption is possible in application using psqlodbc driver.
Also the function returns an undefined error code -8.

The mistake is located here
https://git.postgresql.org/gitweb/?p=psqlodbc.git;a=blob;f=pgapi30.c;h=ba0dd6d731bbccd81392def43ae9b10e9c013aef;hb=HEAD#l1240

Just replace 'ret = SQL_IS_SMALLINT;' with 'rettype = SQL_IS_SMALLINT;'.