I think it's related to the size of th PDF I'm using a PDF file of 360 pages and deplacing a bitmap annotation. and I've got this problem too when barring text (I don't if I should start a new topic for this sorry). The first one what the sample provides and for the second what should be.(made by another pdf editor)
We tested the library with document whose size was 2Gb or 10.000 pages.
I think the issue could be related to some data structure in the document itself.
May you provide your document so we will do some deeper analysis?
I'm am sorry for the long time taken to answer. Below is a sample where it's clear when adding or moving an annotation makes the page blink
I guess the atachement is too large to be uploaded, this is the pdf link :