Gradle Dependency Management - Transitive Dependency Version Incorrect - intellij-idea

Question

I have two projects edited in IntelliJ IDEA 2016 that use Gradle dependency management: project A and project B.
Project A defines a compile scope dependency for elasticsearch as:
compile 'org.elasticsearch:elasticsearch:2.3.1'
Project B declares a compile scope dependency for project A, as so:
compile 'com.mycompany:elasticsearch-common:2.3.1'
I would expect, in the Gradle tool window in IntelliJ IDEA 2016, for project B to see:
...
com.mycompany:elasticsearch-common:2.3.1 (Compile)
org.elasticsearch:elasticsearch:2.3.1 (Compile)
...
Instead I see:
...
com.mycompany:elasticsearch-common:2.3.1 (Compile)
org.elasticsearch:elasticsearch:1.5.2 (Compile)
...
No other dependency in project B depends on elasticsearch, so it's not being overridden by another dependency declaration.
Indeed, the pom.xml on our nexus for project A has this:
<dependency>
<groupId>org.elasticsearch</groupId>
<artifactId>elasticsearch</artifactId>
<version>2.3.1</version>
<scope>compile</scope>
</dependency>
So why is IntelliJ reporting the transitive version for elasticsearch as being 1.5.2?
What I've tried:
Deleting .idea and .gradle inside project B directory
Deleting gradle caches
Invalidating caches and restarting in IntelliJ
Swearing
Drinking lots of tea
Asking friends and colleagues
Emailing Oprah
Reverting to IntelliJ 15 when all of this was fine (now no longer is)
Going to the toilet (related to 5) and hoping it magically fixes itself when I get back
None of the above work.
What does work is specifying the elasticsearch:2.3.1 dependency specifically in project B, but doesn't that negate the entire reason for transitive dependencies?
Any help is appreciated.
Update 1
As suggested by LanceJava in the comments, I ran gradle dependencies to see what was happening.
This shows that it's specifically downgrading it:
org.elasticsearch:elasticsearch:2.3.1 -> 1.5.2
When I ran gradle dependencyInsight on that dependency it came up with:
:dependencyInsight
com.mycompany:elasticsearch-common:2.3.1 (selected by rule)
\--- compile
org.elasticsearch:elasticsearch:1.5.2 (selected by rule)
org.elasticsearch:elasticsearch:2.3.1 -> 1.5.2
\--- com.mycompany:elasticsearch-common:2.3.1
\--- compile
Anyone have any ideas why this is happening?
Update 2
This seems to have the answer: https://discuss.gradle.org/t/excluded-dependence-comes-back-when-spring-boot-plugin-is-applied/17945/2
It seems that the gradle spring-boot plugin likes to take over a bit and enforce it's own dependency versions (even though I'm not using a spring-boot-starter that is using spring-data).
I fixed this by adding:
ext[elasticsearch.version] = '2.3.1'
to my build.gradle file.

Answer 1

What wasn't made clear in the question was that this project was using the spring-boot gradle plugin, which enforces certain versions of libraries, and was force-downgrading my elasicsearch version to keep it in line with it's spring-data requirements (even though I wasn't using spring-data in my project).
I discovered this by executing:
gradle dependencyInsight --dependency elasticsearch --configuration compile
which at the time came out as:
org.elasticsearch:elasticsearch:1.5.2 (selected by rule)
org.elasticsearch:elasticsearch:2.3.1 -> 1.5.2
\--- com.mycompany:elasticsearch-common:2.3.1
\--- runtime
I learnt that the (selected by rule) part meant that something was programatically selecting that particular version. That narrowed it down to being a plugin.
I was only using 4 plugins, being:
java
maven
idea
spring-boot
and the only plugin I hadn't used elsewhere (and therefore hadn't suffered this problem elsewhere) was spring-boot.
Once I commented this plugin out, I could see that the dependency was correct.
At this point I learnt that I needed to explicitly specify the version I wanted to use by:
ext[elasticsearch.version] = '2.3.1'
Sorted. More tea for me!