Hi,
for the archives: the root cause is locale. Both linux/debian servers
were set to the same locale (cs_CZ.UTF-8) but there is slightly
different definition of this locale on those systems - once numbers are
before letters and another time numbers are after letters. Then the
index appears to be broken...
So definitely it's not a postgresql bug. It'd be nice if there are some
safeguards against this mismatch, although I don't know how to do it...
Sorry for the noise.
Kuba