When you go to type a message in chat, the text is invisible UNTIL you get 17 characters into the message (I used two spaces in my test message). UNTIL you get to the 17th character in your message, your message will be invisible. Your 17th character ONLY (So nothing else after the 17th character) will cause your message to FLASH on and off. AFTER your 17th character (so your 18th+ character in your message) will let your message be completely visible with no flashing/invisibility at all. Now it was NOT just that time around, I restarted my Minecraft, and it continued to do this. Also, when your 18th character is in the text box, the back half of the message becomes a DARK GREY color which makes it very, VERY difficult to read. BUT when all text is sent into the text (not being typed and sent) all of these problems aren't there.

I expected to just be able to type in chat without any problems

What happened was the text glitched out... And cause the text to not show properly.
Steps:
1. Open Minecraft 14w28b
2. Open ANY world
3. Start typing (again no text till the 17th character)