This magic AC402b string isn't R1.4 version. 
See links:
https://www.cadforum.cz/en/qaID.asp?tip=868
http://devel.gvsig.org/sites/org.gvsig.dwg/2.0-SNAPSHOT/gvsig-base-library-pom/org.gvsig.dwg/xref/org/gvsig/dwg/lib/DwgFile.html
AC402b magic string
This is a GitHub Issue
repo:libredwg
owner:LibreDWG
Title : AC402b magic string
Issue date:

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This magic AC402b string isn't R1.4 version. 
See links:
https://www.cadforum.cz/en/qaID.asp?tip=868
http://devel.gvsig.org/sites/org.gvsig.dwg/2.0-SNAPSHOT/gvsig-base-library-pom/org.gvsig.dwg/xref/org/gvsig/dwg/lib/DwgFile.html
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