What? Try searching on account suspended/BA audit. These posts often relate to nested tickets as an issue which triggered suspension of the BAEC account. Whilst BA may find it hard to enforce their terms of carriage (and they probably wouldn't want to test this in the courts), they can scrub your avios and tier points and ultimately cancel your BAEC membership.

I am not saying this will happen for a few nested tickets, particularly of the type the OP describes, which involves more than two cities and is only for one week.

If you belive it is tosh, try booking 26 pairs of A-B-A and B-A-B tickets which avoid a fare requirement for a Saturday night stay. My guess is that your BAEC account will be subject to BA audit before you take the last flights.

Anyway, my view is that the OP will be fine, but let's not go too far in saying that nested tickets are never an issue.