Surprising Lightroom behavior

I have a library filter preset called "rectangular" which selects all images having a non-square aspect ratio. As I was reviewing the filter results, I selected one of the images and went to Develop module.  In Develop, I selected the crop tool.  As soon as I chose the 1:1 aspect ratio, the image area went blank.  Back in the grid view of filter results, the rectangular image count had decreased by 1 and the image in question was no longer among the results.  I later found that the selected image had been cropped square without my ever having touched the crop overlay.  Maybe it's not a bug, but it's definitely surprising behavior

It seems to me that, once in Develop, I should be able to make any and all adjustments, irrespective of the Library filter results from which the image was selected. Upon return to the Library module, I expect to see the image missing from the filter results if my adjustments have invalidated the filter criteria.  But not until then.