PHPBB3 forum post save button name is replaced by "preservation draft" for subsilver2 style.
find
[code]value=.quot; {L_SAVE}.quot; [/code]
replace
[code]value=.quot; {L_SAVE_DRAFT}.quot; [/code]
[color=#FF0000] note: altogether there are two places to replace. [/color]
save, upload coverage, login background, update cache, then refresh.