Funny results in query

Hi all,
can someone explain why this is happening?

select field1, field2, field3, field4, field5, field6, field7, field8,
field9, field10, field11, field12, field13, field14 from table where
field18 = 't' order by us_retail_price asc offset 48 limit 6;

returns...
field1
------------+
H1205
B1494
B1496
H1204
B1495
B1497

but ...

select field1, field2, field3, field4, field5, field6, field7, field8,
field9, field10 from table where field18 = 't' order by us_retail_price
asc offset 48 limit 6;

returns...
field1
------------+
H1180
H1179
H1205
B1496
H1204
B1497

it appears the number of fields i have in the select is affecting the
results. I don't understand why?

running 7.2.1

Thanks in advance,
Chris