Why doesn't the Tomcat project immediately reflect changes to servlet classes?

Question

IntelliJ IDEA

Hello.
I work in IDEA 2017.1, I write an application under Tomcat (I use 9.0.0.M19), I test it in the Google Chrome browser Version 57.0.2987.133 (64-bit).
I noticed today one "little thing" when I wrote a servlet to upload a file to the server.
I make changes to the servlet, deploy, the application continues to return an error to me, which, in theory, should not be.
I poked around in the code, tried to find an error, nothing.
Then he made an attempt - completely wiped the project from WabApps Tomcat and IDEA re-spilled it and the errors were gone.
Why aren't changes in servlet classes immediately applied? What's wrong?
ps
deployment settings

artifacts

visually check changes in the directory with classes, the date is fresh

to exclude factors - buffer caching, etc. launched from IE11 (not used before), the problem is reproduced there as well.
In previous versions, it seems that this was not noticed according to my feelings ...

Answer 1

found a solution by activating the reloadable parameter
in particular for this project would be like this

<Context path="/um" docBase="C:\Server\Tomcat\webapps\um\" reloadable="true">
        </Context>