No, the behaviour is quite strange from my point of view.
I did the following steps:

I open the IB_SQL, enter "select * from assay" and click
on 'open dataset'.
The data gets displayed and I move to the last entry.
Pressing the down-key brings me to a new row. I can
edit all fields there. When done, I leave the row with
the up-key. Data gets written to the database.
When I move down again to the new row, I can edit the
char field (name), but not the numeric field (displayPos).

Strange, isn't it?