Currently, if you choose to use the horizontal layout the choices are laid out as if they were one long string of text and any word gap will be used to break the line.

It would be better if "display: inline-block" was used instead. In this case if we run out of room on one line it will split in between the different options, and a new line will always start with a radio button and a new option.

This is particularly relevant on small screen mobile devices, where line-wrapping is more likely.

The style is set on line 18 of mod/choice/styles.css

https://github.com/moodle/moodle/blob/master/mod/choice/styles.css#L18

It's probably like this for historical reasons. IE7 didn't support inline-block.