Easy Forms: unstable behaviour dragging page markers

Originally, my steps to reproduce this were:

• open the standard "multi page form"
• add a text field above the "contact information" page marker
• drag the "contact information" page marker above the newly added field and drop - this works fine
• drag the page marker below the newly added field and drop

Expected: the page marker is now behind the newly added field
Actual: the page marker jumps back above the added field

Trying it again today to answer Mathijs' question it turns out that dragging "up" works, but dragging the field down below the recently added field does not.