The custom build grunt task on master doesn't actually generate custom builds.

Here's a regular build:

~/Projects/jquery:master$ grunt 
Running "submodules" task


Running "selector:src/selector.js" (selector) task
File 'src/selector.js' created.

Running "build:dist/jquery.js:*" (build) task
File 'dist/jquery.js' created.

Running "lint:files" (lint) task
Lint free.

Running "min:dist/jquery.min.js" (min) task
File "dist/jquery.min.js" created.
Uncompressed size: 255395 bytes.
Compressed size: 33506 bytes gzipped (92944 bytes minified).

Running "dist:*" (dist) task

Running "compare_size:files" (compare_size) task
Sizes - compared to master
    255395         (-)  dist/jquery.js                                         
     92944         (-)  dist/jquery.min.js                                     
     33506         (-)  dist/jquery.min.js.gz                                  

Done, without errors.

Here's a custom build:

~/Projects/jquery:master$ grunt custom:-ajax,-css,-dimensions,-effects,-offset min compare_size
Running "custom:-ajax,-css,-dimensions,-effects,-offset" (custom) task
Creating custom build...

Running "build:dist/jquery.js:*:-ajax:-css:-dimensions:-effects:-offset" (build) task
Excluding css              (src/css.js)                  
Excluding ajax             (src/ajax.js)                 
Excluding ajax/jsonp       (src/ajax/jsonp.js)           
Excluding ajax/script      (src/ajax/script.js)          
Excluding ajax/xhr         (src/ajax/xhr.js)             
Excluding effects          (src/effects.js)              
Excluding offset           (src/offset.js)               
Excluding dimensions       (src/dimensions.js)           
File 'dist/jquery.js' created.



Running "min:dist/jquery.min.js" (min) task
File "dist/jquery.min.js" created.
Uncompressed size: 255395 bytes.
Compressed size: 33506 bytes gzipped (92944 bytes minified).

Running "compare_size:files" (compare_size) task
Sizes - compared to master
    255395         (-)  dist/jquery.js                                         
     92944         (-)  dist/jquery.min.js                                     
     33506         (-)  dist/jquery.min.js.gz                                  

Done, without errors.

Notice the filesize hasn't changed. The files are also identical. This happens for any combination of parameters to custom command.