IntelliJ IDEA doesn't redeploy changes

You need to check your run configurations of tomcat, in "Before launch" there should be Make and Build artifact steps, also be sure that all you changed classes are really compiling during redeploy - this is the place I would start from.

Also I don't get why you use redeploy instead of hot-swap? Redeploy is usually same time-consuming as restart server, but hot-swap is nearly instant. Though it allows only to change method bodies and constants, usually it's much prefferable then redeploy in development. Personally I'm using JRebel which is free for non-commercial projects now and restart server very rare.

EDIT: I don't know why your classes are old even after redeploy, but the reason is 99% that they do not compile after changes into exploded folder. Doing maven clean install after each code change is too much (IDE compilation should be enough).

What I can suggest you is not to redeploy but to restart server after big changes. So that IDE perform Make, Build artifact and Deploy artifact tasks.