I know vBulletin is a commercial software, but OPP is their customer, so probably you can deliver the issue to them, if you can't fix it yourselves.

It simply is that the forum uses a custom context menu and this is not helping. While it allows for "Cut", "Copy" and "Paste" like the browsers native context menu would, it block other options, especially the spell correction functionality that is part of most modern browsers.

Strangely enough, the feature of a custom context menu is not active in the "Trouble Tickets" section, but it is active in the "WtA" section, and I guess the rest of the forums. So, I guess it is am issue configuration could solve.