I have unzipped the 2.2.1 file and tried to use the 2.2.1 IDE in debug mode. When I press the debug button I get the following:
A regular compile and upload on 2.2.1 works and the Serial.print inside loop() works.
The same debug compile and load on 2.3.3 does start the debugger and stop at a breakpoint, but Serial.print inside loop() does not work.