Perhaps some code was partly inherited from g2calc :)
1. The cursor is not visible when the focus is on the keypad instead of the entry box, even though things are actually inserted at the cursor when you press keys (I'm not sure it is possible to fix this - at least things ARE inserted at the cursor :) ).
2. The backspace key deletes the last character, instead of the character to the left of the cursor, or the selection (BTW it would be nice to have delete button as well - they could be labelled like this <> )
3. If some text is selected in the entry bar when a button is pressed, the selected text is not deleted.
4. The constant and user-defined function butttons do not work.