Here are some known bugs for 6502sdk:

-Some problems in saving Projects.
-RUN UNTIL RTS doesn't work
-IRQ and NMI don't work
-REMOVE ALL BREAKPOINTS works, bun don't refresh properly the screen
-LOAD MEMORY and SAVE MEMORY don't work. But are they really useful?
-The command TOGGLE BREAKPOINT don't work because there isn't
 anything like a 'current location' in Object window, except for
 the location pointed to by PC. But there is no reason, usually,
 to put a breakpoint in an instruction that is currently being executed...
 ...maybe I'll remove this option.
-Error lines sometimes are wrong (especially in macros)

and...

-the emulator is little more than experimental
-documentation is not complete.

Some other things to do:

-adding an 'extern' declaration to the language, in order to have access
 from a module to another;
-supporting automatic file transfer using RS-232 or Centronics ports;
-making windows refresh faster, using a more intelligent refresh method.
-writing, or getting somewhere, a better text editor.