At the moment editing the name of a tag opens autocompletion which makes it actually quite hard to edit a tag, since you have to remember to press the up key once, because otherwise instead of the edit you actually made, the first autocomplete suggestion is chosen when you press return.
The autocompletion is important to prevent people from (accidentally) making duplicates or variants of the same tag, which greatly diminishes the effectiveness of a tagging system. But you are right on the auto-selection being undesired in this case, we’ll see if that can be suppressed. Thanks!