Will provide description + test-case.
Created attachment 19891 [details] Test-case
Follow the instructions on the test page. Can't select past the WBR using the keyboard. Tested on Safari 3.1 on Windows and Mac.
Interestingly, if, after you place your cursor on the top line, you use the right arrow key to go through the text, it will have a problem at the <wbr>, but you can get past it. Once you have gone past the <wbr>, you are now able to select the text as described in the test case.
Note that this bug makes deleting chunks of text in e.g. Gmail frustrating (once you know the right-arrow workaround you can bypass the bug, but it constantly gets in your way). This is so irritating so often (daily) to webmail users like me that I request this be raised back to P2.
I agree, this is a pretty bad experience and it's surprisingly common to get WBRs in emails.
This actually affects more than just selection. In the testcase on this bug, simply click in the top of the box and use the down arrow to move down. You get stuck at the wbr, just like if you were holding shift. So I think the underlying problem is in the "move down one line" handling.
I tested today attached test case in WebKit r39474 and I cannot reproduce the issue anymore. Bisect-builds tells me that the bug was fixed between r38860 and r39005.