Plain text format and paragraph problem

The line break convertion to

tag don't work with Maxlength and Plain text format info the long text field.

Try to replicate:
on special content type set the body format to plain text and set maxlenght to affect this field (just set the text limit don't check any thing else).
Create a new node and enter many paragraphs, the line break conversion don't work any more.

Desactive the Maxlenght module and go make a modification on the node by adding a other paragraph. What I have is : the line break created when the module was ON are not converted with the

tag so the paragraphs is not showing. The line breaks made when the module was OFF are converted into

tag.

After that go to you content type text field configuration and change the plain text to HTML. The line break will now show correctly into

tags.

How can I use plein text with Maxlenght?