Are you typing your PM in another application like word first so you can spell check it? If you are then you copy and paste the text in to BM it may well come out white. I have just done it and the text was a yellow.
Best thing to do is not to copy and paste the text in. if you want to check the spelling use the ABC icon. It will ask you to install ie spell but you can trust the app. I have been using it for years.
yep it's always word. There's an icon which allows you to paste from Word, but it's not 100% successful every time.
Also, make sure the box turns grey before you start typing. That means it's fully loaded the javascripts