Even though my 8 month old bug report on the same subject was changed to resolved, the issue remains the same as it seems like an additional kind of sleep was added (does not have a status effect icon in client, but normal sleep and deep sleep do).
When using Cast Ninja Spell to place a wind charm field, the field itself only applies the following status effects: Sleep, Silence.
As you can see Deep Sleep is missing from this list as it was removed a year and a half ago or more. This removal was due to the bug fix being done by someone outside RRo staff,(can't find the specific thread on old forums, bug was that status effects were checked every 0.1 second instead of every second)

People never noticed because few people were immune to normal sleep so most people thought that was how it was. But here are some differences between Sleep and Deep Sleep: Sleep makes the next attack hit, doubles crit chance of the first hit, makes the target unable to do anything, but can be resisted by agi. Deep Sleep however disables chat, recovers target's hp/sp every second, makes the target unable to do anything, amplifies the damage of the next hit by 50% and cannot be resisted.

TL;DR
Wrong kind of sleep status effect added, now has two identical sleep status effects. Still no deep sleep.