steps:

run launcher with './minecraft-launcher'

set window size with 'wmctrl -r Launcher -e 0,0,0,1600,900'

close & re-run launcher - launcher window size is 1396x1013 (always)

notes:

• grep'd for '1396' in ~/.minecraft and subdirectories but couldn't find anything related

• tried re-installing launcher from tar file but did not remove or mess with any launcher files in ~/.minecraft