Wrong date displayed for comments

The following screenshots illustrates the problem. A comment written "about 1 year ago" responds to a comment written "24 days ago". Either the order wrong or more likely (following from the content) the wrong date is displayed.

Bonus bug: It shouldn't be possible to save empty comments (like the one by Damien Maier).

Answer in question: https://exams.vis.ethz.ch/exams/tgjzfh4l.pdf#5cfe6a4ebe9eb50010c1814b