Document with 200+ annotations loses newly created annotations

Steps to reproduce:

1. In Web UI configured with NEV, import and view a .PDF document with 2+ pages
2. Through the previewer, add ~200 annotations in varying pages (using different types - e.g. text, shapes, highlight). Note that the issue may occur while attempting to reach this point
3. Beyond 200 annotations, attempt to add annotations in group of ~30
4. Relatively quickly after step 3, press the Refresh annotations button
5. Reload the browser page 

Expected result: on reloading, the preview shows the 30 most recently added annotations.

Actual result: on reloading, several of the 30 most recently added annotations are lost.

If this behavior is not a bug, is there a convention/limit on the number of annotations that can be added to a single document before additions become unstable?