Problem
The monk DV bonus granted (i.e. not taken away) by wearing lightweight armor doesn't consider certain things.

The following items will remove the bonus, despite the fact they weight the same or less than a regular robe (60s).
* fancy clothes (30s)
* ugly clothes (50s)
* blood-stained robe (60s)
* robe of invisibility (60s)
* mummy wrapping (50s)
* ancient mummy wrapping (60s)
* other armor whose weight is reduced to 60 stones or below via the "light" prefix (leather aprons only?)

Furthermore, body armor that does grant the bonus always does, so regardless of any weight-altering prefixes. For example, an ultra-heavy robe (480s) will still work.

Proposed solution: check the total weight of armor, rather than the item type.

How to reproduce it
With a sufficiently advanced monk PC, get some of the above-mentioned items, and compare your DV when equipping them.

Notes
N/A