Is this a bug of C# IDE

This is the scenario:
Open a cs file for editing. Spliting the window. Edit the file in lower part of code window. Then try to rename a variable in upper part of window with typing. Normaly that a rename mark should be shown and with mouse click or shortcut i can activate rename action. But in this case that doesn't show any more. Even when i remove the split of file, or try with diferent variable. That behaviour is lost for good from that point on. I need to close the file and open again to have such behaviour of rename assistance from IDE.