🚀 go-pugleaf

I have code which looks like

Select * from PERSONAL p , LINKPERSADDR lpa, ADDRESS a , LINKADDRTELE lat,
TELEPHONY t
where  t.UPPERPACKEDNUMBER Starting With "0385316661"  and
p.PERSONALAUTONO = lpa.PERSONALAUTONO and
lpa.ADDRESSAUTONO = a.ADDRESSAUTONO and
lat.ADDRESSAUTONO = a.ADDRESSAUTONO and
t.TELEPHONYAUTONO = lat.TELEPHONYAUTONO
order by p.UPPERNAME

On one machine running IB 8.1.0.257 this returns a plan of

PLAN SORT (JOIN (A NATURAL,LPA INDEX (LINKADDRPERS),P INDEX
(RDB$PRIMARY5),LAT INDEX (RDB$PRIMARY24),T INDEX
(UPPERTELEPACKEDNUMBER,RDB$PRIMARY6)))
which is using Natural on ADDRESS A and is terribly slow

But on a different machine running IB 8.0.0.123
version
I get a plan of
PLAN SORT (JOIN (T INDEX (UPPERTELEPACKEDNUMBER),LAT INDEX (LINKTELEADDR),A
INDEX (RDB$PRIMARY1),LPA INDEX (LINKADDRPERS),P INDEX (RDB$PRIMARY5)))
and very fast.

All indexes exist on each machine.

Why are these two different plans generated. I don't particularly want to
add a plan statement to the statement as this is generated on the fly and
would need many conditionals to build the correct plan each time.

Any help appreciated

Regards

Peter