All items within migration are rolled back when --sync is set and source plugin $trackChanges is set to FALSE

Problem/Motivation

I am yet to get to the bottom of this issue but here are my findings so far:
- When I run a SqlBase‑based source plugin migration with trackChanges set to FALSE—and that migration has already run (so all items are in place)—every item gets rolled back and migrated again.
- When I rerun a SqlBase‑based source plugin migration with trackChanges set to FALSE—and that migration has already run but some items have since been removed from the source—those removed items are rolled back, and no items are migrated again
- When I run a SqlBase‑based source plugin migration with trackChanges set to TRUE—and that migration has already run (so all items are in place)—no item gets rolled back and migrated again.
- When I rerun a SqlBase‑based source plugin migration with trackChanges set to TRUE—and that migration has already run but some items have since been removed from the source—those removed items are rolled back, and no items are migrated again

The first one is obviously incorrect, adding trackChanges = TRUE seems to correct the behaviour to the expected one. However, I don't think trackChanges should be a requirement.