Bug or not ?

I'm writing a C program using libpq.
The part of code:

res=PQexec(conn,"create table aaa (num int4); insert into aaa (5);" );

PostgreSQL returns error: "table aaa does not exist"
And table aaa is not created.

Same error appears if to write a 'select * from aaa' instead 'insert'.

BUT
res=PQexec(conn,"create table aaa (num int4); create table bbb (num
char);" );
OR
res=PQexec(conn,"create table aaa (num int4); drop table aaa;" );

are work OK. Tables are created and dropped.

Is it bug, or not ?