Although the text editor of the Effective Altruism Forum works well for most users, occasionally people have problems with text formatting.
The main trick is to be careful of text that you have pasted in from another document. When you paste text, its original formatting is preserved and this will generally not match the rest of the forum. You can correct the text by correcting the html by hand, or by using this site to convert your html to plain text.
This may be just me, but it would be handy to be able to input in markdown as well as html. It seems pretty common to have editors that accept both.