(are you really seeing a semi colon between them? or (Bowman et al., 2003) (Terras, 2006) and do the two independently turn “gray” when the cursor is in them? If they are,
This is usually caused by inserting each of the citations separately and having a space between them. if you remove the space, they will join as you want them to be, when you import another citation or update citations and bibliography.
(Bowman et al., 2003; Terras, 2006)
You also said:
By the way, the Harvard style template has a typo in the Citation Template: it says (Authorl; Year) instead of (Author, Year).
That is not a typo. It is a “separate” character and prevents the loss of the trailing parenthesis if you didn’t have a year (which is pretty unlikely). There is another special character the link adjacent, which is also critical in many cases, especially if it is adjacent to a field that may be or maynot be filled/used. – it prevents random punctuation and spaces appearing even if the field is absent.