Hmm, that sounds something like a PHP issue that we've seen before. Can you look at your phpinfo page and see if you have any varfilter settings in there such as:
varfilter.max_array_depth 100 100
varfilter.max_array_index_length 64 64
varfilter.max_request_variables 600 600
varfilter.max_totalname_length 256 256
varfilter.max_value_length 200000 200000
varfilter.max_varname_length 64 64
