On my server, when I turn survival-breaking-creative: deny: false, drop-items: false, players are able to break absolutely everything in sight. The strange thing is that block simply vanishes from the slightest hand swing; with no sound, no effects, it just disappears, and even logging plugins don't see this event, worldguard and towny cannot protect it too because they don't see this event just like the logging plugins. You cannot even roll it back with the logging plugins.
Very weird stuff. As soon, as I turn deny: true, everything turns back to normal, with the difference that I have to manually clear the creative mode littering everywhere because regular players cannot break the creative blocks. Kinda annoying. Hope you'll fix it soon.
Thank you!

Cannot reproduce.

It appears you have another issue with a different plugin. AntiShare when configured to allow survival players to break creative blocks will let them complete the entire break sequence before doing it's check on if he block should drop items or not.

The setting that you chose simply tells AntiShare to not drop any items when a creative survival player breaks a creative block.

Closing as cannot reproduce/bad configuration/other plugin.