raising concerns about what other odd things were done with the wiring.
You are right to have such concerns. My experience in rewiring older homes is that everyone who lived there before you was an idiot when it comes to wiring, and did crazy stuff for you to discover.
As others have said, it could be a two-hots-shared-neutral circuit. You should carefully determine if that is the case. If it is, then you should understand the consequences of having such a circuit in your house, particularly the consequences of making changes to your wiring. I say this from experience; every house I have helped someone rewire (including my own) that had such a circuit had it wired in the unsafe configuration. Moreover, upon doing some archaeological analysis, it appears that in each case the circuit was originally wired safely, and then rewired by homeowners into an unsafe configuration later.
The important thing to understand about such a circuit is that you are required to have the two hots on opposite phases in the circuit breaker box. The reason for that is: the current on a circuit is by definition the same at every point; that's what makes it a circuit. If you have two hots sharing a neutral, then the current on the neutral is the sum of the current on the two hots if the hots are on the same phase, and the difference of the currents if they are on different phases.
Consider the consequences of that. If you have two 15 amp breakers and a 10 amp current on both hots, then the current on the neutral is 10 + 10 = 20 if the hots are on the same phase, and 10 - 10 = 0 if on opposite phases. That is, in the unsafe configuration there is a 20 amp current on a neutral wire that is rated for 15 amps, but neutrals are not protected by the breaker, so the breaker will not trip and the neutral will get warm, possibly very warm.
If the person who installed the circuit did so correctly, the two hots will be on opposite phases, and ideally will be forced to be on opposite phases by the use of a double-wide breaker. But if they are on two single breakers, what then happens is that homeowners do not realize that the phase of each is an invariant that must be maintained, and in the course of some change to their wiring, move one of the breakers to the same phase without understanding the consequences and produce an unsafe situation.