Safari 'Easter Egg' imposing CSS overrides ***?!

I've noticed this bug/feature in Safari at least three times now and it has overridden the display of three web sites that I can recall. Latest one was Apple Communities and a restart of Safari hasn't helped. Even if a re-boot fixes the situation (haven't tried yet but I'm not overly-optomisic based on prior experience of the bug).

I'd like to get some answers, surely I ain't the only one suffering this.

It always starts with me placing the cursor in a text field, or seeing the cursor blinking in a text field (not 100% sure which) and me starting to type.

Before I've finished a word or two the page background goes Pink coloured and many of the major link texts are underlined with a thin purple line. I grabbed a picture this time:

As I type a few letters this Safari 'feature' seems to be executing a few shortcuts according to the letters I type.

Notice the "Set text size to 14.0" text pop-up in bottom left corner in the above image.

In all case of experiencing this bug I've ended up with Helvetica Text overriding the preferred text of the page. This also happened to me when browsing Facebook and a lot of text sizes got hosed too.

After re-clicking in the text field and entering text things return to normal but the text stays overridden.

What on earth is going on?!