Ahh, after finally being able to figure out this "strange bug" it turns
out it is the application's own fault. It wrongly assumes it is running
on a feature phone and tries to map digits on characters all by
itself rather than having the platform take care of it. So it more or
less maps characters this way

1:
2: abc
3: def
4: ghi
5: jkl
6: mno
7: pqr
8: tuv
9: wxyz

Tapping twice on 3 gives you an "e". So it has nothing to do with
"i" and "t" being swapped or whatever.

The fact that you have to tap this special arrow button, is just due
to the way you have to enter digits on the N900. So this is no bug
in my port, but rather a 'feature' in the Facebook app itself!

Davy