vector ligation problem

[huazhongw]

Dear memebers,
       I am working with  vector constuction. I inserted a fragment into a vector by routine single-digest \electrophoresis\recovery\ligation\tranformation method. When I recut recombinant plasmids with the same enzyme, I run into a problem that the vector fragment size become smaller than the original cut vector.
       I don't know why and need help!


Huazhong Wang