I seem to be having an odd issue with BOM numbering in drawings.

I have a drawing from which I have created a BOM from the final assembly listing all the items in it. I have selected follow assembly order and follow sub assembly order along with do not change item numbers. Great everything lists as it should.

I then create a second drawing I insert the same final assembly to create a BOM however a couple of the item numbers are switched around.

Where as on the previous drawing the BOM would read 24, 25, 26 etc I now have 24, 26, 25. I untick don't change item numbers and the numbers go into order, but as soon as I hide some rows due to unticking that box the item numbers change which I don't want them to.

I have attached two images to illustrate. What I can't work out is why on one drawing the BOM lists fine with all  the options selected, but on the second and other drawings I get a BOM like picture 2

Any ideas.