convertToCapped copies in _id order
What changes in convertToCapped copies in _id order compared with MongoDB and what your application has to do.
This difference is of the Different kind.
What MongoDB does
It copies documents in insertion order.
What TeselaDB does
It copies them in _id order, so, if the collection is over the size, different documents survive.
What your application has to do
If you need to choose which ones remain, trim the collection yourself before converting it.