The nice thing about only syncing a mirror is that it only consumes disk space, which is pretty easy to get -- usually. After all, my current laptop is 10 yrs. old and has 37GB.
(It's an experiment, so that's all right. I renovated it with linux for fun.
) But most new computers have much more than you need.
Regarding a change to calibre -- IIRC Kovid did this deliberately, on the grounds that it takes too long to keep recreating a new format, and tossing the copy would mke it difficult to debug problems. But he may be amenable to a change, assuming it is a setting. It would help a lot in edge cases like this. That would seem optimal to me, as any user advanced enough to set this should be aware of the compromise.
If not, I am sure you could create a plugin hook to do this.
