So I found 2 more bugs (in the interpreter part of the extention rather than the live part)
1) show_message()
and some other stuff doesn't automatically convert real to string (original GM function does)
2) inst.value = other_value
doesn't work
luckily, as a user you can find workarouns (use variable_instance_set() and string() functions), but this still might be a bit annoying and hard to debug (it just silently crashes/doesn't execute code after a complile error)
Here's the example string: