Changing G/L account in Purchase invoice line reset unit direct cost

Hi,

maybe it is a dumb question but can't find a setup or a way to avoid it.

Navision 2017

I create a purchase invoice, as line invoice i used

type: G/L Account

No. : my gl accouunt

Quantity : 1

direct unit cost : 100

then i realized that i wrongly choose the G/l Account .

As soon as i change it , the direct unit cost is deleted and set to 0 ( but not quantity) , is there a way to chang G/L account without loosing the direct unit cost amount ?

Tks in advance

Fabrizio