Bashed/Merged Patch not really merging properly?

[gurgle166]

I'm quite new to bashed/merged patching but my understanding is that it's supposed to merge plugins and not just have one overwrite the other fully.

So to test, I made one .esp mod increasing Thump-Thump's value by 1000, and a second .esp mod decreasing its weight by 3. The idea is that a merged patch should be able to merge both changes and result in Thump-Thump having both increased value and reduced weight, right? I tried with FNVEdit and the automatic merged patch function there just made an empty .esp file, while with Wrye, the resulting bashed patch just had a change to the weight while the value change was completely thrown away and overwritten.

What's going on? Am I doing something wrong? Aren't these changes supposed to be merged? What's the point in patching if one change is just going to overwrite the other anyway? Thanks for any help that could be provided.