I often render my timelapses out of Lightroom with the preset "filename-image sequence" which lists the original filename and a -1, -2, -3 etc. at the end of each file. This has always worked with Vegas' "open image sequence" until recently. Now the box remains greyed out.
Magix, please allow that box to be checked any time we select more than one image, so there is a workaround even if Vegas fails to detect that there is a sequence.