GNU cash crashes when I try to link an invoice to a payment on account

[andy]

Hi,

can anyone tell me why GNUcash vs 2.6.5 on Lubuntu 14.04.1 crashes 
whenever I link a payment on account with an invoice.

I would have a payment linked to a customer then also have an invoice, 
and then business/ customer/ process payment and highlight both payment 
and invoice so payment amount is zero. At this point Gnucash just freezes.

It also freezes if the payment amount is negative. This means I can't 
apply forward payments to invoices and so invoices don't get paid and 
customers have huge unapplied amounts.

Is this a setup problem or generic bug for developers (which I can't 
help with sorry)

cheers

andy