I am not sure if this is a bug or a feature. Also, is this is a Page Builder or JCE Editor Pro issue.
When inputting HTML code into the Content portion of the Text Block Add-in, I use the "Code" tab do do this. If I then hit Save and exit, any changes are lost. I must first switch to the Editor tab before saving. Obviously, going to the Editor tab to save is a work-around, but it is also a pain to remember and not how I would expect this to work.