I a recent post I wrote that under some circumstances a database compact on a Domino 8.5 server can corrupt java applets in the database design.

Today, IBM support confirmed this as a bug:

Hello,

I was able to reproduce the issue you reported following your steps to
recreate.
This seems like a bug alright. I am going to create a new Software Problem
Report on this issue which will be brought to the attention of Level 3.