I only noticed this for the first time yesterday in RC6 (although it may have occurred earlier), and have confirmed that it is still occurring in RC7.
Ensure you can print to two printers (I print to a Brother Laser, and to PDF).
Open a document and select File/Print Current Document/Print - Scrivener will print to the prior selected printer Open a document and select File/Print Current Document. Change the printer to the alternative and press Print. Scrivener ignores the change in printer.
As a work around you can File/Print Preview. Change the printer to the alternative by clicking on the printer icon at the top and selecting the alternative printer. Press Print and Scrivener will print to the changed printer. And as per the bug Scrivener will then continue to use this printer until you change it again in Print Preview.
Further annoyance was that the print dialogue box is very small and appears almost out of sight at top left of the screen and doesn't remember where it is repositioned to.
On the print preview dialogue, I couldn't at first see the printer icon. It took very careful searching to see the little arrow at the right-hand side which on clicking, made the printer icon appear on a second row, The print preview box did however appear centre screen but it would be good if it appeared large enough to show all the icons.
I wish to add a remark concerning the strange useability of the printer dialogue box in RC7.
My Windows 10 (1903 version) lists several printers, mainly Microsoft print to file stuff. Although they have never been used, they do appear in the list of printers.
I couldn't at first see my HP laserjet listed in the RC7 printer dialogue box which is pretty small and appears top left on my screen. It took me a while to find the scroll feature to look for my printer. Then I realised that it was a horizontal slider used to effect a vertical scroll of the available printers.
This is, in my opinion, an unusual and non-intuitive feature in a GUI system and should be corrected to be a vertical slider preferably on the right-hand side of the dialogue box.
I understand that this may not be considered a bug of sufficient importance to warrant fixing prior to the release of the full version 3 but it might be possible to correct while looking at the underlying printer selection bug identified by the OP above.
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If so, it is the default Windows system print dialog. It is not a part of Scrivener. Scrivener uses the Windows print API to launch this. This is the same for many other programs - Notepad++, for example, calls this same dialog to print. Scrivener 1.9.x calls this same dialog.
Well ... you live and learn, don't you? That is the dialogue box to which I referred. Sorry, but I didn't realise that was the standard default Windows printing dialogue.
I very seldom print anything on paper and have never printed from Scrivener, mainly because I am not a fan of Scrivener's formatting so I transfer my projects to LO Writer for that job. I only tried printing in RC7 to test the OP's bug (first post above).
Neither Microsoft Word nor LibreOffice Writer uses this dialogue box in Windows 10. Their dialogues have vertical sliders for vertical scrolling of printer selection. I don't have Notepad++.
The bulk of my work is carried out on a Linux box and I just keep the Windows 10 box for applications like Sibelius and Scrivener. I have used Scrivener in Linux, both the older Linux version and the Windows version under Wine but Scrivener for Windows certainly runs better and looks nicer in the W10 box.