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.