Thank you for your report. The bug is known.
The cause of this was the old system of weapon selecting in NaS and the addition of a second musket to the units.
Unfortunatly in Betatesting we didnt catch the bug, as at the time of the last patch, there was only a small event left, which was only line anyway. For the same reason it wasnt fixed, to not further hurt the population of NaS with another update, people would have to install.
For the time beeing, just change to another class and then back to the sapper/arty/marine, and you should spawn with the correct equipment.