Issue relates to all Printer Driver Languages (PDL) - PCL 5, PCL 6 and Postscript. Whenever a print job has multiple pages wherein the first page of the job has a defined MEDIA SIZE and MEDIA TYPE and subsequent pages only define MEDIA SIZE - all three PDLs will use the MEDIA TYPE defined for the first page.
Example:
Microsoft Word > Page Setup > Paper Tab
First Page is defined as -
Media Size = Monarch
Media Type = Envelope
Source = AutoSelect
Second Page is defined as -
Media Size = Executive
Media Type = [Unspecified]
Media Source = Tray 3
In this example, Page 1 has both MEDIA TYPE and MEDIA SIZE specified. Page 2 only has MEDIA SIZE specified. Therefore MEDIA TYPE [Envelope] is inherited for remaining pages. Because Tray 3 doesn't support the specified MEDIA TYPE, device prompts "Load Tray 1: Envelope, Exec"