I've always just accepted it as something that could be improved, but to me, it doesn't seem to be a bug. It isn't behaving in a fashion contrary to the documentation, it doesn't lose or corrupt my data, it doesn't behave unpredictably or crash the program. If that screen had other similar spots for entering data, and this was the only one that didn't allow editing an existing entry, I still might not call it a bug, but I would certainly be pushing for improvement to equal functionality!
It's clearly something that could be improved. If that is important to you, you know the drill, Send Feedback or email
omnifocus-iphone@omnigroup.com so they know you want them to improve it. I spend more time entering test contexts to answer forum questions than I do making changes to my own context locations, I think! I prefer to direct my votes towards changes that will have a bigger impact on me, or the occasional changes that I think really ought to be made even if they won't affect me.