Subform not showing correct data

[P]

I have a form with two levels of subform on it, reflecting the hierarchy of
tables;

Customer - Primary index is serno, contains details about the customer

ContactLine - Primary index is contactlineid, has foreign key to Customer.
Contains details about an individual transaction

ItemLine - Primary index is itemlineid, has foreign key to Contactline.
Contains details about the items in an individual transaction


My form shows Customer details, with a subform showing the contactline
transactions for that customer. The Contactline form has a subform showing
itemlines.

Customer and ContactLine seem to work well. When I press the button which
exists on the ContactLine to create a new ItemLine, it updates the ItemLine
table correctly, but the data shown in the Itemline subform is the data for
the previous Contactline. If I move off that ContactLine record and then
back on, the Itemline subform then shows the correct data.

I've been playing all day on this, with no success. Has anybody seen this
problem? I've tried adding Requery commands in various places (AfterUpdate
on the ContactLine, for example), but with no success.

Regards,

Pete.