Two block high flowers breaking

All specifically player placed two block high flowers( including double tall grass and ferns) where found either on the ground in item form or with the top half missing, in which the bottom half would soon break and drop in item form as well.
this was found on a SMP server hosted by myself shortly after copying the world from a 1.7.10 server which ran on an .exe server file, whereas the new server is a .jar file. possible problem source?