Thanks for the answers and the fixes.
I opened the fixed files, they seemed to show correctly. I now know that it is LibreCAD fault that fails to follow the dxf standard strictly. Because you already know how to fix the file issue, will you add this feature to ZCAD? LibreCAD has good amount of users, if ZCAD can open LibreCAD files without issue, you will gain more user base.
Polar tracking is good but it cannot fully solve my problem. It only accepts length and angle of 45 degree increments. I do not know the others, but in architectural drawing we often need to use relative x, y coordinate. For example how can I do relative coordinate for @20,25 using polar tracking?
ZCAD doesn't have pdf export. It is very important, LibreCAD has built-in pdf export. Please consider to add this feature.
I noticed ZCAD does not always show grid if I zoom very far or close. It is very important because I draw things with dimension ranging from several meters to hundreds of meters. It should automatically set the grids 1x, 10x, 100x, ...
Sorry I asked too much. I really hope I can to use ZCAD instead of LibreCAD. I saw ZCAD has some features that makes it better than LibreCAD. For example LibreCAD uses MDI, which makes switching between drawings hard.