Here's a bug with []FMT with a really long format string. Bug occurs in APL versions 5.2.10 and 6.0.10 (and probably others).
foo
© Execute this several times
© Note the strange (and changing!) suffixes on the right edge
© 21 Sep 2006 Rex Swain, Independent Consultant, www.rexswain.com
c„1863
f„',< >,O¯2147483647< >CI14,< |>'
f„1‡(c×½f)½f
m„f Œfmt (3,c)½¼999
Œ„'Left:'
Œ„ Œpw †[2] m
Œ„'Right:'
Œ„(-Œpw)†[2] m