I also noticed text being shown where it should have been 'hidden'. I came to the forum to see if anything has been reported about it and found this topic.
I use 'hidden' characters (color 1,1) in my server MOTD which are now shown and make everything look improper. I used them with good reason:
In the old days, I used to make a lot of drawings, usually lighter colors on a black background; I filled every line with the same amount of characters to get a nice black rectangle around it to make it look good for viewers using a white background. At first I used spaces to fill the empty space with blackness, but then I noticed there were IRC clients/addons that cropped multiple spaces to one single space. This problem could be solved in two ways: I could give every space a new colorcode to not have those clients/addons crop the multiple spaces. But that made drawings a bit hoggy, since the client had to parse a colorcode for every character. It also made lines very long and limited the possibilities. I chose for the second way: to use different characters than a space to fill my drawing. It didn't matter what characters I used to fill empty space because you wouldn't see them... But with the latest change in the beta, you do.