The composition engine assumes that an uppercase letter followed by a period is part of an abbreviation and follows it with an inter-word space. For abbreviations that end in a lowercase letter, like "no.", it assumes that the period is the end of a sentence. You can use "&nbsp;" after the period instead of a normal space to get back the inter-word space (for example "no.&nbsp;3.", but this will no longer be a valid break-point.