When using proxy my request is set to HTTP/1

Using the library httpx which allows me to make HTTP/2 request to target sites.

However when I use the proxy it seem to automatically set my request to HTTP/1.

I.e

async def main():
    client = httpx.AsyncClient(http2=True)
    response = await client.get('someurl', headers=headers)
    print(response.http_version)

This prints HTTP/2

But same thing using proxy like so client = httpx.AsyncClient(http2=True, proxies=someproxydictionary)

it prints HTTP/1

Why is this behavior happening only when routing through proxies?