Clean waits forever w/non-standard buildDir

With debug logging on, I can see the clean Deleter is trying to remove a non-existent gradle folder because it is disregarding my provided buildDir in the root buildscript, although it properly used it to produce output. Here is the output of my gradlew -v:

Gradle 2.13-rc-2

Build time:   2016-04-19 14:52:40 UTC
Build number: none
Revision:     3b427b1481e46232107303c90be7b05079b05b1c

Groovy:       2.4.4
Ant:          Apache Ant(TM) version 1.9.6 compiled on June 29 2015
JVM:          1.8.0_92 (Oracle Corporation 25.92-b14)
OS:           Windows 10 10.0 amd64

For example, in the root buildscript specifying

buildDir = new File("C:\build")

will produce all gradle output correctly in that directory. However, the command

gradlew desktop:clean --debug

hangs forever, with the final line of the log being

16:08:36:960[DEBUG] [org.gradle.api.internal.file.delete.Deleter] Deleting C:\code\dev_branch\build\desktop\gradle

Additionally, the command

gradlew --stop & rm -rf %HOMEDRIVE%%HOMEPATH%\.gradle\caches\modules-2

hangs for a very long time before proceeding (minutes), then fails to remove the directory because files are in use. TaskManager shows no java / gradle / non-system processes running, and gradle reported all daemons stopped successfully. Logging out/in and repeating the same command succeeds.

Any ideas what’s going on here?

I found a very similar bug report, but the suggestions there don’t seem relevant to me.

NOTE: I have access to rm -rf on a Windows console because GowTools are installed.