First this is clearly not a bug. Feeds generated by WordPress are ordered by post publication date, which is both intended and makes sense.
Second RSS clients uniquely identify items. In specific case of WP feeds unique identifier is guid field with non-pretty (?p=xxx) permalink. Even if post is changed and brought back into feed its identifier remains the same and it is treated as read by RSS client.
In practice some clients will detect is as changed, some won’t. In any case situation will be ambiguous and unreliable.
From usability point of view previously read items re-appearing in feed can be annoying to readers (for me personally it’s annoying like hell).
To sum it up what you want is not impossible but (in my opinion) goes against both WordPress and RSS mechanics.
Given your conditions (and I assume considerable amount of such edits) I would suggest periodic digest posts with lists of updated entries. Can be generated manually or by code.