aiomysql: Query returns result from another query

Here is my problem. I use aiomysql in aiohttp handlers. Something like this:

async def handler(request):
    data = await get_data(request.app['db_pool'])

async def get_data(db_pool):
    # prepare query q and params
    async with db_pool.acquire() as conn:
        async with conn.cursor() as cur:
            await cur.execute(q, params)
            rows = await cur.fetchall()
    # do something with rows
    # and return result

And some times rows are not the result for the given query q but the result from other query. There are no errors. It just silently returns wrong result. The only way i could determine that situation was that queries had different number of fields so there was an index out of bounds error in the log some times.

So the question is - do i run it in a right way? Or should i use any locks somewhere? Or is it a bug in the library?