Same happens for the simpler

while true do c+=1 end

This occurs because in this case, the "do" does NOT have a matching "end";
apparently the grammar for while lets you have a newline, a colon or a do there. 

The same thing is true for until (until false do c+=1 end).

I think the root bug here is that JRuby returns the wrong token for "do" in the
above case - I get a Tokens.kDO instead of a Tokens.kDO_COND. Since I get a kDO
I look for a matching "end", which "while" also does, so it's missing an extra end.

Reassigning this issue to newly created 'ruby' component.

This is fixed for the simpler case (while true do c +=1 end) but still broken for the case where while is not first on the line.

Try to put this code inline:
th = Thread.new{while true do c+=1 end}

then push enter in between while and true for example:
th = Thread.new{while <enter> true do c+=1 end}

It will produce sth like this
th = Thread.new{while 
    
endtrue do c+=1 end}

Still valid, needs to be fixed in jruby-parser.

Still there. My previous comment about that this needs to be fixed in jruby-parser is not right; I guess the comment was meant for another issue.