Bash not finding shell script in first directory on path

[maarvarq]

Further to my Lilypond woes...

Lilypond is installed (I just had to re-install it but that's another issue) and there is a lilypond shell script as promised in my /home/mark/bin folder

mark@mark-GA-MA785GMT-UD2H:~$ ls /home/mark/bin
abc2ly      lilypond-book            midi2ly               sfarkxtc
convert-ly  lilypond-invoke-editor   mup2ly                uninstall-lilypond
etf2ly      lilypond-wrapper.guile   musicxml2ly
lilypond    lilypond-wrapper.python  RealPlayer10GOLD.bin

and this folder is the first one in the PATH variable
mark@mark-GA-MA785GMT-UD2H:~$ echo $PATH
/home/mark/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/share:/usr/share/lilypond

but bash isn't finding it there
mark@mark-GA-MA785GMT-UD2H:~$ lilypond O_Sacrum_Convivium_MC
bash: /usr/bin/lilypond: No such file or directory

It runs fine if I specify the directory for the command
mark@mark-GA-MA785GMT-UD2H:~$ /home/mark/bin/lilypond O_Sacrum_Convivium_MC
GNU LilyPond 2.14.2
Processing `O_Sacrum_Convivium_MC.ly'
etc. so this isn't insuperable, but am I missing something obvious or should this not be happening? Thanks.