I can't duplicate any issue like that.

Instead of Dm/C, use Dm7/C

I just tried it with _BOSSAG, and it plays fine.

But I also tried it with Dm/C and it played fine there too. (by fine, I mean the guitar plays a nice syncopated pattern, not 4 quarter notes. In fact the guitar pushes into the bar, which is nice.

I also tried it with another bossa style _BNGGRMD (Med Bossa w/Piano NY), and that was fine too.
(both of those styles are accessed from the "Band" button, which is a feature of 2012, but of course you can access them from the StylePicker too.
You can hear that here http://nn.pgmusic.com/pgfiles/jazzu/misc/BossaDemo23.WMA
and the sgu song that made it here http://nn.pgmusic.com/pgfiles/jazzu/misc/BossaDemo23.SGU

It is just playing this:
Dm Dm7/C E7/B
using the style _BNGGRMD (Med Bossa w/Piano NY)

So I need to know what style you are using, and what chords. Perhaps there is something in the song (a style change, time sig change etc.) that is causing the issue.

Perhaps send the song to support@pgmusic.com if you are still having problems.

Have Fun!
Peter Gannon
PG Music Inc.