I've always used full power, too. This last microwave that I've had is the only one that has a specific button for melting butter. In fact till today I didn't even know that butter exploded. I never heard of such a thing.
I did have a neighbor that set her brand new microwave on fire by melting butter when microwaves were something new. I asked her how in the world she did it and she said that she set it for 5 minutes. As far as I know she never bought another microwave, thank God.