Inconsistent line spacing

Question

If I type something like this:

{\itshape\LARGE
  Dunt venim dolorerosto do odit
  ametum vulla conum dolore
  conulput in vero od el
  Dunt venim dolorerosto do odit
  ametum vulla conum dolore
  conulput in vero od el
}

it results in a block of 4 lines with narrow spacing between the 1st and 2nd line and between the 3rd and 4th line. Line spacing between the 2nd and 3rd line is normal.

I can't fully explaing it to myself so I am looking for a short description for this behaviour. I know for example that with a \par at the end of the text (inside the group), the calculation would correct. But I have no idea why...

Answer 1

Make sure to end the paragraph (using \par, for example) before leaving the group; compare:

\documentclass{article}

\begin{document}

% wrong    
{\itshape\LARGE
  Dunt venim dolorerosto do odit
  ametum vulla conum dolore
  conulput in vero od el
  Dunt venim dolorerosto do odit
  ametum vulla conum dolore
  conulput in vero od el
}

% right    
{\itshape\LARGE
  Dunt venim dolorerosto do odit
  ametum vulla conum dolore
  conulput in vero od el
  Dunt venim dolorerosto do odit
  ametum vulla conum dolore
  conulput in vero od el\par
}

\end{document}

The reason why a \par (or some form of paragraph ending) is needed is that \LARGE (and the other font size changing commands) changes the the value for \baselineskip and \par is the command that ends the paragraph and applies the right \baselineskip.