Photoshop Is Saving As Illustrator Not As Photoshop

Photoshop seems to be saving as an Illustrator file on my computer. To be clear I don't want it to. I create a Photoshop progect and I save it in the normal way, IE File/Save As/Save on my computer. I save it with the .psd extention and ... it saves with an Illustrator icon with the .psd suffix on the file name. Well, perhaps there is a glitch and the two programs are sharing an icon for some reason. So I click on the icon and it opens in Illustrator despite having the .psd! If I go into Photoshop first I can open it as a normal PS file but I'd like to know why PS and Illustrator seem to be mixing together during the saving process. Has anyone else had this problem?  I am running a fully updated version of Windows 10 Pro on a computer with an AMD processor. This is the first time I've had this problem.