With more testing I found that the context menu position depends (perhaps solely) on whether my mouse pointer is on the left side or the right side of the horizontal half of the rightmost monitor: if you imagine a vertical line dividing the rightmost monitor’s display area into two equal-sized halves, right-clicking anywhere on the left side of that line brings up the menu on the correct display, whereas right-clicking anywhere on the right side brings it up on the wrong display.
(That is why I first made the mistake of thinking links weren’t affected: the ones I tried first just happened to be on the left side.)
Unfortunately I don’t have a third display to verify that I’m really seeing a different manifestation of the same bug as Nathaniel, of one that depends on the monitor count.
Spoke too soon: looks like the context menu for links just also turned affected. I swear they still worked correctly when I was writing the previous comment!
I can reproduce this on a two-monitor setup: right-clicking in Chromium on the right monitor brings up context menu on the left monitor. Right-clicking on the left monitor works as expected.
I cannot reproduce the workaround: here the context menu opens on the left monitor no matter how close to the right edge of the right monitor I right-click Chromium.
I recently upgraded from 12.04 to 14.04, and this issue appeared with the upgrade. 12.04 currently has Chromium 37.0.2062.120, whereas 14.04 has version 44.0.2403.89.
Upstream has a similar bug report about right-clicking links , but for me at least right-clicking links is *not* affected: the issue occurs only for the tabs’ context menu and for web page right-clicks outside links, whereas the context menu of links opens on the right monitor.
Also, LP bug #1430393  looks related, and is also reproducible here: (left-clicking) the main menu button also opens the menu on the wrong monitor.
*  https://code.google.com/p/chromium/issues/detail?id=409287
*  https://bugs.launchpad.net/ubuntu/+source/chromium-browser/+bug/1430393
Not speaking for The Chromium Projects or anyone, but I think the things you mention are just not considered issues to be addressed in the project. The Chromium Projects are, by their own words, ”open-source”, which by FSF’s definition (as also mentioned in one of the threads you linked to) is different from free software. Barring any actual non-free licensing issues, any party with an interest to do so should, in my understanding, be able to branch a new project from Chromium and address those issues, turning their branched codebase into what the FSF and Trisquel would then consider free enough to qualify.
In other words, these aren’t issues to be fixed ”by Chromium”, but by parties with an interest to have them fixed. And at least according to G4JC at the aforementioned thread, it would be quite a substantial amount of work to be done.
This morning Gmail notified me that my browser is unsupported, which made me realize Chromium for Precise hasn’t been updated since September 2014 and is currently at version 37 (37.0.2062.120-0ubuntu0.12.04.1~pkg917) whereas more recent versions of Ubuntu are already at Chromium version 41. The ”unsupported version” messages are of course harmless and easy enough to dismiss, but I’m guessing the newer Chromium releases also have important security fixes that should warrant an update – unless there are compatibility issues blocking it from happening?
Reopening. It didn’t go away after all, looks like the occurrence varies (didn’t see it yesterday), perhaps those Chromium settings just made it more probable.
I take that back, it seems to have been caused by Chromium all along (more specifically either #threaded-compositing-mode or #deadline-scheduling), despite those glitches appearing outside of Chromium too. Sot it’s a Chromium bug, but I’m too lazy to debug this further (the issue goes away with those configuration flags set to default) so I’ll just mark this as invalid.
Also, here’s a screenshot (from the video) with the artifacts visible. I notice they seem to cover mostly just Chromium’s content area, but just last night I had this occur just as I was logging out (with the lines remaining on screen until I tried to take a screenshot), with nothing but the log out confirmation running on top of my desktop, so it’s probably not just Chromium that’s causing this.
3. Vim, Gedit
4. Gmail (on the web)
6. Screen, yes
I have Trusty and Precise installations affected by this. For me just one refresh usually is enough to fix it though. Also, sometimes the blackening doesn’t happen straight away but only once I start scrolling the page down to the comments section.