Why custom web.config isn't loaded?

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Visual-Studio

web.config

I try to solve this trouble for 3 days and i think i need your help guys. I use VS13.

I made some custom configs, under Web.config. The process of made is as usual with Configuration Manager and "Add Config Transforms". Lets call one of my custom configs "Custom1". So i made Web.Custom1.config.

In this config i insert only that conncetionstrings,appsettings and client options that i want to replace using replace transform and match locator, i.e. xdt:Transform="Replace" xdt:Locator="Match(key)"

Everything look fine. I choose the config from "Solution Configurations", build successful without any error. After build i look into XML Configuration in the windows folder and each key,address,name and everything is replaced correctly.

And now when I want to Start something is wrong. I use a breakpoint to see, what is matched to the ConnectionString. To my surprise the ConnectionString.Value is localhost o.O.

Now my question is why? What i made wrong, what i need to do. Why after build the config looks fine and after Start, config "returns" to localhost? I read a lot of solutions but no one help me.

I will be really grateful if someone help me and tell me (pref in steps :P) what should i do. Thanks a lot.