Say I have 10 files loaded sorted by track number. If I select the file on line 2 of the file display (i.e. track 2), enable the filter so that another file is now occupying line 2 (e.g. track 10), then disable the filter, now track 10 on line 10 is selected instead of track 2.
Another issue is that if I select some files then enable the filter with a filter expression which has zero matches with the currently loaded files i.e the file list is now empty, then immediately disable the filter, the previously selected files are no longer highlighted. This doesn't seem to happen if the filter expression has some matches. One way to re-highlight the selected files is to do a column sort.
However by doing repeated filter enable/disables (whether there are any matches or not) followed by successive various column sorts, the number of files selected (both the status bar count and the highlighted files) can be increased (and sometimes decreased) randomly.
I think observations 1 and 3 are connected.