When using a single File[] parameter like:

#@ File[] (style="extensions:tif/tiff/ims") files

.. we always show a file chooser dialog using chooseFiles.
Only when a second unrelated parameter is added, a file list widget is shown in a generated input dialog:

#@ File[] (style="extensions:tif/tiff/ims") files
#@ String (required=false) ignoreThis

There should be a possiblity to get an input dialog with the file list widget, without the need to add secondary parameters.

(I thought I had opened a ticket about this long ago, but I couldn't find it, so here it is.)