Changes to the NTVDM - DOS-printing?

We have problems with one DOS-based accounting application on Vista
Business, i.e. printing to more than one printer. There are no
problems from within XP Pro/SP2.

All three printers (2 OKI 293 and 1 Minolta laser) work fine from
Vista.

This works from the command line (cmd.exe and command.com)

dir > lpt1
dir > lpt2
dir \\sbs\minolta

Any mapping does also work, such as:

net use lpt3 \\sbs\miolta /persistent:yes

However, from within the DOS app only lpt1 works. Also XP Pro on VPC
on Vista works fine with printing.

Is this a bug? Are there documented changes to the NTVDM on Vista
except no support for full-screen mode with the WDDM?

Thanks in advance!

jas