Steps to reproduce:

1. Copy a table from a web or Excel source (use the files in attachment if needed: mytable.odt and mytable.html) and paste it onto a richtext field on creating a content;

2. Click as if after the pasted table inside the richtext, as if to add something else after it, and click the "+" button, and choose to add a paragraph.
The paragraph will be added inside the last cell of the previously added table.

3. Now click again near the end of the table (the "+" symbol should move lower) and try again to add a paragraph. It will work now.

Try to repeat the previous steps using a table from an Office Word source. The problem will not occur. You will be able to span a Paragraph right at first try.
Having to execute these steps twice may induce in error that it is actually impossible to add something else after a table on richtext field.