Issue: Unable to change tags?

There is no problem in adding tags while creating an article but when I save that article I will face strange problem in editing the tags.

Below articles, I can add or remove(uncheck) tags but after saving it I don't see any changes in the tags! I click on edit again and I see the latest changes that I have made but this is only in edit mode.
In other words, after creating the article tags can be changed but the preview of tags remains the same.


(vB 3.8.4)

btw, when is the expected release date for vw3.1.0?

thanks,