If I have some nested functions, the call tip will sometimes move around when the cursor moves between the functions.
This happens when you are typing in new text. It also happens when you place the cursor in the middle of a line of nested functions, press CTRL+SHIFT+SPACE to display the call tip, and then move the cursor to the left or right. When the cursor crosses into a new function the tool-tip jumps up to the top-right corner of the screen.
If you have the above line of code and place the cursor where the underscore is and press CTRL+SHIFT+SPACE, the call-tip for substr will appear.
Now move the cursor to the right until you pass the closing parentheses. The call-tip for decode will now appear, but in the top-left corner of the screen.