Once an editor is activated, it handles the keyboard and mouse input. That is why the cell's tooltip is not shown.
The following code snippet demonstrates a sample approach how to show a tool tip when a RadTextBoxEditor is initialized. The attached gif file illustrates the achieved result. Note that this is just a sample approach and it may not cover all possible cases. Feel free to modify and extend it for the other editor types in order to achieved the desired custom behavior.
I hope this information helps. If you need any further assistance please don't hesitate to contact me.
Dess | Tech Support Engineer, Sr.
Progress is here for your business, like always. Read more about the measures we are taking to ensure business continuity and help fight the COVID-19 pandemic. Our thoughts here at Progress are with those affected by the outbreak.