PC Lockup under DOS with PC/XE board & read string

I am running a PC/XE 8-port serial card configured at 9600 baud with polling only. This system is running under MS-Dos. If the system is booted and characters are sent to port 1 before the boot-up completes, the port is unusable. In fact, the application locks up as soon as the port is accessed for a read string call. We are using the DOS int-14 call for clearing the port and reading a string. These calls will work with the older DIGI COMM/XI boards but has stopped working with the PC/Xe boards. Why? Also, the int-14 calls to read character by character do not show this problem. Any ideas?
This is also posted under hardware.