Very strange figure when posting VAT in foreign currency

alsol

Hello everybody,
We have a very strange problem which does not make any sense to me:

We posted some invoices using the Sales Journal. The entries looked like this (LCY is CHF):

Acc. Type: Customer
Acc. No.: AD100002
Curr. Cd.: RUR
Amount: 660'000
Amount (LCY): 30'054.42 (was not manually changed)
Currency Factor: 21.96016426202868
Bal. Gen. Post. Type: Sale
Bal. Acc. Type: G/L Account
Bal. Acc. No.: 3102
Bal. VAT Bus....: RU
Bal. VAT Prod...: RU18

Everything looks fine. After posting this entry, the LCY (CHF) amounts are all correct. On the FCY side we have the entry on A/R and on the income account which both are correct too.
But the entry on the VAT amount has a FCY amount of 559'322 which is not the VAT but the VAT base amount. How can this be possible? It seems that Navision used a Currency Conv. Rate of 0.0081 instead of 0.045 just for the VAT entry. And as soon we run the Currency adjustment G/L report we have a huge difference.

Has anyone any ideas? :-k