When a pre-formatted paragraph with long lines is displayed in VE it word wraps. However it doesn't word-wrap in display mode (T2260), meaning that you have no idea that you need to add manual line breaks until after you have saved.
See https://en.wikipedia.org/w/index.php?title=User:Thryduulf/sandbox3&oldid=573792519#Section_number_three (rendered) and https://en.wikipedia.org/w/index.php?title=User:Thryduulf/sandbox3&oldid=573792519&veaction=edit§ion=2 (in VE)
The word wrapping in VE is actually better than what happens in read mode, but the two should not be different. Fixing T2260 would be better, but as it's been open since 2004 adjusting VE to match the current behaviour seems more realistic :/