"Cannot insert multiple commands into prepared statement" issue while executing query with params

(python 3.5.1, asyncpg 0.5.4)

Consider the next code

import asyncpg
import asyncio

async def run():
    con = await asyncpg.connect(user="coldmind", database="test")
    await con.execute('SELECT ($1); SELECT 2;', 1)
asyncio.get_event_loop().run_until_complete(run())

The executing fails with asyncpg.exceptions.PostgresSyntaxError: cannot insert multiple commands into a prepared statement error, while the another example (without passing params to the query) works well with multiple commands:

import asyncpg
import asyncio


async def run():
    con = await asyncpg.connect(user="coldmind", database="test")
    await con.execute('SELECT 1; SELECT 2;')
asyncio.get_event_loop().run_until_complete(run())

Why is the first example using a prepared statement instead of executing it?

Start with the con.execute entry point and run the two Python examples from the issue to compare parameterized and non-parameterized queries. Trace how parameters affect execution, then establish the expected behavior for multiple commands and document or test the resulting decision.