If you use djgpp 1.12.maint3, get and install 1.12.maint4 maintenance release. 1.12.maint3 had a bug in one of the library routines which would cause these problems under XMS driver (such as himem). Alternatively, you could install a VCPI server like emm386 or qemm386, or work under DPMI (like Windows), because that problem doesn't appear in these environments.