query_posts() clobbers get_query_var()

I’m new to WP, so maybe this is expected, but it seems weird to me that using query_posts before get_query_var seems to not work correctly.

This code:

query_posts('posts_per_page=-1');
$nn_lat = get_query_var('nn_lat');
$nn_lon = get_query_var('nn_lon');

always returns the empty string from get_query_var while this code

$nn_lat = get_query_var('nn_lat');
$nn_lon = get_query_var('nn_lon');
query_posts('posts_per_page=-1');

works correctly.

Is that the intended behavior?