Normally in DOS times there is only one point in the filename to split the fileextention. Now 40 years later you can use many Points in a filename. But Sketchup make a mistake. It cuts the filename by the first point, in title bar and file dialog box,
“A.B.C.D.skp” converted to “A” and not correctly to “A.B.C.D”
If you uses Point to give the your filenames a structure, you are very surprised.