Field "options" of existent menu items is overriding on any changes, but there can be some data stored by other modules. For example, Menu Icons module stores additional classes in "options" field. So, if you change term, its menu item will loose menu icon.
And more, if your taxonomy menu contains nodes count, attaching/detaching nodes to term will erase "options" too.
Patch fixes this problem, so we can create taxonomy menu, attach icons to menu items and then edit terms. Patch was made from 6.x-2.8.