This issue seems to have reappeared in prerelease 5.  I placed both a yellow and regular shulker box in single player world and both disappeared when breaking the box without using any tools.  The yellow box contained items and the plain box was empty.   I then tried breaking the empty shulker box with different tools (pickax with silk touch, pickax with fortune, ax, sword) and the shulker box still did not drop on being broken.

This is single player world which was created in 1.17 and upgraded to 1.18 release 1 and then to 1.18 release five.  The world was in peaceful mode and had cheats enabled.  This occurred in survival mode.  This is java edition.

I tested it for a new game created with release 5 and the issue does not seem to occur.