When track changes is enabled, MS Word transposes characters when using the wildcard string (a.k.a. regular expression):

Find \(([0-9]{4})\)

Replace with . \1.

The aim of the string is to transform, e.g. Hart, Keith (1973) to Hart, Keith. 1973.

But when track changes is on it produces Hart, Keith1973..

The only way to work around this that I know of is to turn off track changes for the duration of wildcard-driven find/replace operations.

Thanks to PCReview for providing the solution.