Illustrator Save As PDF overwrites the original .Ai document

I create a normal AI document. Make my graphic and save it as an AI document. In the course of my work, I need to send something to my client and save the document save as .pdf.

As if by magic, the AI_Document has now become a pdf document. I have lost hours of work this way if you don't notice.

This stupid and absolutely not comprehensible behavior sucks. That's why I save the document: save as and don't just save the document.

For this behavior it now urgently needs a patch! Immediately! Thx

{Renamed by MOD}