What's going on here?

Can something this simple really be so wrong? Here's a simple query in SQL Anywhere 11.0.1.2276 that returns 5 rows, starting at row number 10, from a table t where pkey is the PRIMARY KEY column t, and that column is DEFAULT AUTOINCREMENT with values 1, 2, 3...:

SELECT TOP 5 START AT 10 *
  FROM t
 ORDER BY pkey;

pkey,data
10,'B'
11,'B'
12,'B'
13,'B'
14,'B'

So far so good... now supposing we add WHERE data = 'B' to the query; shouldn't the result set be the same?

But it's not! Look here:

SELECT TOP 5 START AT 10 *
  FROM t
 WHERE data = 'B' 
 ORDER BY pkey;

pkey,data
15,'B'
16,'B'
17,'B'
18,'B'
19,'B'

What's going on here? Clearly rows 10 through 14 have data = 'B', why aren't those rows showing up in the second query?

This is a bug in SQL Anywhere 11.0.1.2276, right?

For the answer see Well, don't leave us hanging... is this a bug or not?