A very annoying bug that was introduced earlier this year (or may have been late 2018) and doesn't seem to have been fixed.
When I insert an image from the images manager it inserts the image I want, as well as all the previous images from the same article, in an accumulative manner.
Steps to reproduce:
Upload a selection of images into the manager > go back to article > find a place you want to insert the image > click 'insert image' icon > select your first image > click insert.
Inserting the first image is OK
Now put your cursor where you want your second image to go > click 'insert image' icon > select your second image > click Insert.
Expected result: Only the selected (second) image should be inserted
Actual result: Both the first and second image are inserted.
Repeat the process choosing a 3rd image. Now the first, second and third image will be inserted so you have to go through deleting the ones you don't want in that position.
The only workaround is to drag in each image individually but sometimes this isn't really possible.