Hi. First, you don't really need gzip, since GNU tar can manage compression on the fly. You need it only for some older Unix flavours. Moreover you can omit the -z (for gzipped files) option since tar determines the kind of compression automatically:
$ tar zxvf UIMA12.tar.gz
$ tar zxvf m1.tar.gz
However there is not an explanation for your issue, except for the fact that the two archives actually contain a different directory structure. What is the output of the following commands (with t in place of x)?
$ tar ztvf UIMA12.tar.gz
$ tar ztvf m1.tar.gz
Please post only the first lines of the output if it is long and please use code tags to improve readability. Thanks.