ID numbers jumping

Ok got a problem the support people don't seem to want or be able to help with

over the last couple of weeks the ID numbers of a call raised have jumped by a still amount some have been by 200 i.e call raised ID assigned 200 next call raised sometimes minutes later id assigned 400.

the support desk keeps sending me some sql to run and asks for the results

select * from workorder_threaded where thd_woid>7234

i send the results and i get told the call has been merged with another call int his case i got told 120 + calls had been merged with another call.

I get an email raised everytime a call is raised and surely for a call to be merged it needs to be raised?

I am getting no help from the support people so has anyone seen this got any ideas..

TIA