68 - invisible/uneditable text in MultiLineEditBox

What steps will reproduce the problem?
1. Define a multi-line edit box in AceOptions ( {type="input",multiline=true} ) and set some text for it.
2. ???
3. Profit!!!
4. The text in the box is invisible and cannot be edited normally, but in some reports can still be copy-pasted in one or both directions.

This has been reported by at least 4 different users of two different addons (Auarcle and Pitbull), both of which use AceOptions to create the edit box in question. It doesn't happen to everyone, and I don't know of any reliable way to reproduce it, but here the various reports:

http://wow.curse.com/downloads/wow-addons/details/auracle.aspx#532517
http://www.wowace.com/addons/auracle/tickets/18-text-of-auras-field-not-visible-editable/
http://www.wowace.com/addons/pitbull4/tickets/438-dog-tag-text-edit-box-not-showing-text/
http://www.wowace.com/addons/pitbull4/tickets/566-lua-code-window-turns-blank/

I glanced at the MultiLineEditBox widget code and didn't see anything really obvious, but did notice some slightly odd trick played in :SetText() (with the comment "prevents OnTextChanged from firing" -- maybe this prevents the container from refreshing, so the text is there but never gets drawn?).