In wysiwyg, cannot type text after a mention, if the mention is the first thing in a paragraph

To reproduce:

• type in a page content, in the Wysiwyg editor
• at the beginning of a paragraph, type @ , and then choose a user name
• the mention will be added and transformed in a macro

Expected result:

• after the mention, I want to add some text to tell something to the person that I just mentioned

Actual result:

• the mention macro seems to be a block macro, occupying the whole line and I cannot place the cursor after the mention macro to type something on the same line.
  

I reproduced this on a 12.9-SNAPSHOT from the 10th of October.