Samsung 830 and ZFS TRIM

Hello,

(initially posted this to -questions_at_ a week ago, w/o reply)

I installed CURRENT on a new Thinkpad equipped with a Samsung 830 SSD:

ada0 at ahcich0 bus 0 scbus0 target 0 lun 0
ada0: <SAMSUNG SSD 830 Series CXM03B1Q> ATA-9 SATA 3.x device
ada0: 600.000MB/s transfers (SATA 3.x, UDMA6, PIO 8192bytes)
ada0: Command Queueing enabled
ada0: 122104MB (250069680 512 byte sectors: 1H 63S/T 16383C)
ada0: Previously was known as ad4

as the setup is ZFS+GELI based (on ada0), I enabled ZFS TRIM support in 
loader.conf.

Interestingly, I encounter an IMHO strange behavior with the stats on that:

kstat.zfs.misc.zio_trim.zio_trim_bytes: 755712
kstat.zfs.misc.zio_trim.zio_trim_success: 97
kstat.zfs.misc.zio_trim.zio_trim_unsupported: 7891
kstat.zfs.misc.zio_trim.zio_trim_failed: 0

It seems unintuitive to me why the unsupported counter first increases 
(seems to stay constant after that each boot) and then slowly the 
success counter increases as well.

Probably there is a trivial explanation (GELI?) and/or fix for this that 
anyone is willing to share?

If you need further information, let me know.

Thanks a lot

Johannes