Why does forms with single input field submit upon pressing enter key in input

This is a little known "Quirk" that has been out for a while. I know some people have resolved it in various ways.

The easiest bypass in my opinion is to simply have a second input that isn't displayed to the user. Granted not all that user friendly on the backend, it does work to resolve the issue.

I should note that the most common place that I hear of this issue is with IE specifically and not with FireFox or others. Although it does seem to affect them as well.

This is a known bug in IE6/7/8. It doesn't appear that you will get a fix for it.

The best workaround you can do for this, is to add another hidden field (if your engineering conscience permits). IE will no longer auto-submit a form when it finds that there are two input-type fields in the form.

Update

In case you were wondering why this is the case, this gem comes straight out of the HTML 2.0 specification (Section 8.2):

When there is only one single-line text input field in a form, the user agent should accept Enter in that field as a request to submit the form.