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"It's too late for Germany" (but not for Poland) [1798]
Even if Germany were to pay, the next Polish generation would just demand more money.
That is actually the main reason behind the no-talks....these things are over and done with or else the EU couldn't had been build. If one country starts to re-think the old treaties again it would open flood gates. Everybody could now demand reparations for every grievance ever happened...that hasn't has to stop at WWII....there are raw wounds till barely scabbed over all over Europe, and some wounds are still quite open.
One of the prime demands by the EU for new members is the closure of conflicts first. As the EU doesn't want to "inherent" the old, ongoing grievances of it's new members, especially when all of the involved party's want to become members...that's no-no for very good reasons, such fights between members could destroy the EU.
To restart an old conflict, demand border changes or reparations won't happen after membership!
That's primarily the reason that there won't be any additional money exchange just because the political mood in one member country changes. Poland would have to leave the EU to keep it's demand alive! The same with Greece btw...
PS: A good current example is the name conflict between Greece and Macedonia (or what it will be called). A conflict stemming from centuries of history...but without its resolve Macedonia won't become a member either of EU nor NATO.
en.wikipedia.org/wiki/Macedonia_naming_dispute#NATO_and_EU_accession_talks