Starting with a side note:
@>~" ^\n"
~"SyntaxError: invalid syntax\n"
&"Error while executing Python code.\n"
@
This looks like the version of python your gdb uses is too old from Qt Creator's point of view. 2.6 is minimum. You won't have much fun with that setup further down the road.
Having said that, the breakpoint setting should work. The issued commands are ok, and work in a similar setup using "stock" GNU gdb (GDB) 7.0.1 for me (just tested)
@>31^done,BreakpointTable={nr_rows="1",...],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x03f1b4d5",func="pluginTest",file="simple_test_plugin.cpp",fullname="/data/dev/creator/tests/manual/debugger/simple/simple_test_plugin.cpp",line="40",times="1",original-location="\"simple_test_plugin.cpp":40"}]}
@
Are you sure your .so has debug information?