If a user has set specific texture format for working on a platform other than the one they are developing the RenderTexture asset can auto select another format since it might not be supported on the current dev platform. This also means if you use a windows only format, then move the project to OSX and then back to windows you are not guaranteed to have the same format you started with, as it will go through 2 lots of falling back.

Steps to reproduce:
1) Create RenderTexture asset
2) Change the format to R32G32B32A32_SINT

Expected result:Unity attempts to make the format, if it cannot on the platform it then falls back to something and tells the user through UI, keeping the original choice serialised.
Actual result:Unity falls back to what it can and writes it to the file, losing the users choice and serialising different data which might not be wanted when deployed.

Note:Errors are always displayed when the RT is being used and it falls back to none, not sure if this is ideal.

Repos in 2019.1.0a14