The case of the disapearing picture

The strangest thing I have ever seen in Lightroom.

I have a picture that does not show up after I used filters. 

This picture (and the virtual copy) are flagged and have stars. If I use the filter to show me the flagged pictures, it does not show up. Even worse, if I turn of the filters... the picture is gone. 

If I look for it by number in the folder it still does not show up.

Only if I look for the number of the picture in the folder above the folder where it should be, I can see it apearing and if I right click and 'go to folder in library' it will show up again in its (sub)folder.

I noticed this because it did not export with the edit I made on it. So something went wrong there too.

Also, reimporting or syncing the folder did not help me with the problem.

Has anyone seen/noticed this before?

I sure hope this is not happening often without me noticing it, and missing out om some great shots.

Thanks.