Any time you paste in text from a word processor application (Word, Pages, etc.) it also copies in hidden formatting code. This code gives very inconsistent results among various web browsers and between platforms.
You should only use plain text inside RW and use the formatting features of RW to do the actual formatting.
You can do this easily with pasted text if you use the menu command “Edit -> Paste as Plain Text” when you paste any text into RW.