Printing 6 3/4 envelope

Linux Mint 17
This may be a printer driver issue. I have hp c5200 series printer. When trying to print a standard (or is it?) 6 3/4 envelope that I set the page size to in writer, the printer says ‘paper size or type is incorrect’. If I look at the printer properties, there is no 6 3/4 envelope form. Printing with other page size works if it’s in both writer page size and printer form.

This has been reported as bug fdo#77149. Sounds similar to this question about #10 envelopes reverting to a different size. I hope it is not because there are still various open bugs for that issue.