OJP 7740 does not print duplex

New OJP 7740 using HPLIP prints test page as one duplex sheet. But 2-page (8-1/2 X 11 plain paper) print jobs print two 1-sided sheets of paper rather than one 2-sided sheet as requested.

One job was a 2-page spreadsheet document successfully printed as one 2-sided (duplex) page on a Brother printer. Prints as two 1-sided pages on 7740.

A second job was a freshly created 2-page (each page with a single line of text) word processing document that prints as two 1-sided pages on 7740 instead of one duplex sheet.

A third job was a 15-page PDF file of which pages 1-3 were were requested to be printed. They printed as expected on the 7740: pages 1 & 2 duplexed on the first sheet and page 3 printed on a second sheet.

A fourth job was a 6-page spreadsheet document with a request to duplex print pages 1-3. This worked like the third job above...as expected.

A fifth job was a 6-page spreadsheet document with a request to duplex print pages 1-2. This worked like the first job described above -- giving two single-sided pages rather than the desired one 2-sided page.

So am I right to assume this printer can only print in duplex mode for jobs greater than 2 pages? If not, what am I missing?

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