allow-transfer not covering ixfr requests?

[Torsten Segner]

I recently observered a rather strange phaenomenon.
By accident I have configured a nameserver to allow queries from NS1 and NS2 and allow transfers from NS3 und NS4.
So far so good... 
Naturally NS1 and NS2 could do all kinds of queries but no zone transfers.

NS3 and NS4 weren't allowed to ask anything but were able to request axfr transfers.

The odd part is that both NS3 and NS4 weren't able to request ixfr transfers. 
Shouldn't allow-transfer cover these kind of transfer requests as well?


Ciao
Torsten


PS: All nameservers are running on a self-compiled 9.8.1