Message kept in the "sending" state

Hi @ergo_404, can you let us know:

1. Which version Mattermost you're using, and if you upgraded recently (Main Menu > About Mattermost will tell you the version)?

2. What browser are you using?

There was a bug reported in Mattermost v1.1.0 with Safari 8. Mattermost v1.2.1 now requires a minimum version of Safari 9 and we're not seeing the issue any more.