Thanks to Cyril* I have just solved a weird problem I had with Typo. To write my posts, I use Markdown. When I began to use Typo I did not know how I could use Markdown. First, I simply wrote in the visual rich editor but then Markdown was not taken into account. So I used the ‘source’ mode, there it was working. Except that the carriage returns where not displayed by this view. So, as long as I was typing the post it was ok but when I wanted to go back to a post it was really ugly. Thus I saved my posts in a text file and if I wanted to update one I updated the text file and copied and pasted to typo. You imagine the pain !
I have long thought this stupid problem was due to a bad configuration. Somehow it was. A way to solve this problem is to go to Settings/Write and choose ‘Use simple editor without live preview’ instead of ‘Use visual rich editor’. The catch is with that you won’t be able to have a … ‘live preview’. There is at least one other person wishing a ‘live preview’.
I am glad to have Typo fully working now !

* To be precise Fred also helped me on this subject some time ago but his answer, while correct, was not precise enough and I had not understood it, my bad. Thanks all the same !