"When I pluck a string with I/A finger they kind of bounce back to the start posision by themselves,but when I pluck with M finger it stops half way out,I have press it out to the start posision.This happends when I move the fingers slow."Troubleshooting anything like this is a bit like untangling the spaghetti on someone's plate with a blindfold on :-) A video would help.
What if you play with M by itself? (ie not in combination with any fingers). If you pick up the guitar, gently pluck an open string with M and feel it relax does it return (however slowly) to starting position?
The sensation of the finger 'emptying' completely of tension once it has played is important. The trouble is it only takes a tiny amount of tension to hold a finger in a slightly flexed or slightly extended position and it is very easy with FD to not notice that tension is there.
