BBCode: Adds new linefeed each switch from source/preview: [/list] [u][url=http://snap...../]Updates[/url][/u]

[Alan Welsh]

Steps to reproduce

Recreated in both Firefox and Edge on the CKEditor BBCode Samples page.

1. Go to ​http://sdk.ckeditor.com/samples/bbcode.html and paste this into a blank SOURCE window:

[list]
[*]test
[*]test
[/list]
[u][url=http://snapback-apps.com/updatewindows/]Manage My Windows Updates[/url][/u] - Controls Windows 10 Updates without the work, hassle or risk.
[list]
[*]test
[*]test
[/list]
[list]

2. Switch to PREVIEW, and it appears with an EXTRA linefeed:

test
test
           <<<<< Should NOT be added here!!
Manage My Windows Updates - Controls Windows 10 Updates without the work, hassle or risk.
test
test

3. Switch back to SOURCE, and you will see a new linefeed has been added to source.

NOTE: This will NOT add a new linefeed if the line after [ /list ] is just text. (I didn't test any other types of content.)

4. Go to PREVIEW, and yet another linefeed has been added, each time you switch to PREVIEW.

Expected result == NO new linefeeds added when switching from source to preview

Actual result == One NEW linefeed is added with each switch

Other details

Related: Other issues with line breaks: #7870, #10078, #11524, #7870.

Costs / workarounds for users

Must always go back into the source and delete the number of linefeeds by hand. How many? An extra linefeed is added each time you switch, so the number of corrections will always be 1-x for each time you use both [ /list ], followed by a URL on the next line