Formatting of large posts

[TheFull9]

I'm just finalising a fairly sizable review here before I post it but the software is being a right pain.

 

I click preview and it decides to just stick double-line spacing everywhere there was single line spacing before (i.e. between all my paragraphs and images). Also, every time I go down to the content entry box to try and adjust and correct this, said box shows the spacing as being single line (in both editing modes) but when I click on said single line it disappears down to zero lines, and I have to manually move the cursor to the full stop at the end of the previous paragraph and input another blank line in every single space. Click 'Preview Post' and it all gets just as messed up as it was when I started again.

 

Also hitting the Preview button magically vanishes any YouTube videos that I embed in to the new thread OP. Images are fine and unaffected but I've no idea how the actual post will come out looking if it just get it looking right in the content entry field and simply hit 'Post New Topic'.

 

Any insight in to what I'm perhaps doing wrong would be much appreciated.