Hi qsun,
1. I can reproduce this problem.
2. Editor remove the <br/> before the first <br/> did not generate any format for the content.
For example the text below, the first <br/> did not generate any format because it at the end of the <div> target, so when you try to remove the empty line, the <br/> be removed too.
<div>this is a test<br/>
</div>
<br />
test
I will report it to the development team, once issue is fixed, I will keep you posted. Sorry for your inconvenience.
Regards,
Ken