2018.1 on windows 7 x64. Merge Maps from multiple subtools doesn’t seem to work with the MultiMap Exporter plugin.
I reinstalled 4R8 and merge maps is working from there. 
I also noticed two other bugs; when merging all subtools (uv checked) with levels (reconstruct subdiv), it breaks the uvs.
And the curvebridge brush rescales the ztool (or unifies it?) and affected subtools.