Browser will open external link.
Obsidian search for tag:#twittertag is opened
OSX11.2 0.10.12
Workaround: Move # outside of link. That’s not nearly as nice though. #[twittertag](https://twitter.com/hashtag/twittertag).
Putting a backslash before the hashtag results in the link opening correctly in preview mode.
[\#twittertag](https://twitter.com/hashtag/twittertag).
This is a dirty fix, the behavior you experienced does appear to be a bug.