Can you elaborate or provide a URL?
Infoboxes should automatically size based on the window content, so height:auto won’t do anything.
To check if you have a theme conflict, you can switch to the 2013 theme for a moment.
If you’re using infoWindows instead of infoBoxes, there’s a bug in the Google API that sizes them wrong. Star this issue to have Google fix it (they seem to prioritize by number of stars):