Serializing a specific object is writing twice the content to file in most of the tries

[sn4k3]

I'm getting a very stange behaviour where my serialize is put twice the content of the class into file. I search and try some alternatives but without success. Sometimes it wont happen but in most of cases it is.
The problematic object is a sub object inside a class, but same sub object is used on other classes that never duplicate the content.
If i try serialize only that object (without the parent class) the same still happens.

On image i have the original on LEFT and saved on RIGHT, look that LAYERDEF (Section class) is duplicated when shound't.

Main class: https://github.com/sn4k3/UVtools/blob/master/UVtools.Core/FileFormats/PWSFile.cs#L710
Sub object class which duplicates: https://github.com/sn4k3/UVtools/blob/a2e2f5c7f3afa9263d9ad1a9cbc0673d5d86cfe4/UVtools.Core/FileFormats/PWSFile.cs#L141
Serialize line: https://github.com/sn4k3/UVtools/blob/a2e2f5c7f3afa9263d9ad1a9cbc0673d5d86cfe4/UVtools.Core/FileFormats/PWSFile.cs#L1040