I'm pretty sare the new "central European" entrants to the EU were given a derogation on their Russian aircraft for a period of time from entry, from memory it was 3 years but I stand to be corrected? Then there's a separate issue of where in the EU they would be allowed to fly into due to airport noise regs. I remember talking to one company in Lithuania in 2004 who were running Antonovs and told me they had every intention of operating them as long as they could before they had to switch to BAe/ATR/whatever freighter, which would cost them more to run. I'm sure any of the guys who run the local freighter operations in those countries could give you chapter and verse.
The Bulgarian situation had more to do with the lousy standards of the operators, and complete inability to come up to some kind of acceptable level both in ops and paperwork, than the aircraft type they were flying.