Edit: This seems to have been resolved.

Bug overview description.
Uncaught TypeError from PostMenuMode.click() when you click within the bounds of a span.thumb without navigating away from the page. No incorrect behavior observable outside the console.

What part(s) of the site page(s) are affected?
Pages which have thumbs but do not have the Mode menu it would seem. Specifically observed it on /post/popular_by_day and on user profiles.

Can you reproduce the bug every time?
Yes

What steps did you take to replicate this bug?
Just click on the .post-score or elsewhere in the span that won't navigate away.

Errors or other messages returned (if any).

application-min.js?1500132206:formatted:13974
Uncaught TypeError: Cannot read property 'value' of null
    at Object.click (application-min.js?1500132206:formatted:13974)
    at HTMLSpanElement.onclick (popular_by_day:249)

Can not reproduce this. I suspect it may be related to an extension. If you can reproduce it again and gather more information, let me know by posting in this thread.