It seems that it doesn't work on the commented part of the line, that is, spaces after ; are NOT converted to tabs. Is it by design or a bug? I'd prefer all the line be converted ...

It is by design, as editor convert only spaces that are not syntax highlighted. This was done this way, so that for example spaces inside quoted strings would not get converted. I agree this kind of solution has a bad side effect that comments don't get compressed. I may still think about some other design...

i noticed that tabs (09h) [not sure about some cases with spaces] before CR/LF (db 13,10) sometimes are left in source, while i think they should be removed.