I would like to ask for clarification about Twitter sharing in iOS 11 onwards.
The official Apple documentation states in the release notes the following:
The people from twitter answered my question. It seems to be a bug right now:
https://twittercommunity.com/t/bug-in-ios-11/91490
However, it's still unconfirmed if this will be the default behavior for iOS 11.
EDIT:
The issue was fixed in version Twitter.app (7.7.2)
EDIT 2:
For clarification, this behavior should no longer occur if the user has the Twitter.app (version 7.72 and up) installed, since the sharing window is actually provided by the Twitter app. (Same as Facebook sharing)