FULL PRODUCT VERSION :
java.runtime.version 1.8.0_66-b17

ADDITIONAL OS VERSION INFORMATION :
Mac OS Yosemite 10.10.5
10.10.5
Darwin Kernel Version 14.5.0: Tue Sep 1 21:23:09 PDT 2015; root:xnu-2782.50.1~1/RELEASE_X86_64 x86_64

A DESCRIPTION OF THE PROBLEM :
The Java Mac OS Launcher is not using the Xmx value specified in:
/Users/USERNAME/Library/Preferences/Bloom.plist.
There's no Bloom.plist under /Users/carl/Library/Preferences/

The application started has the following app id: Bloom
-Dapp.preferences.id=Bloom
-Xmx1024m
-Xms512m
This was verified using JVisualVM

Under /Applications/Bloom.app/Contents/Java/Bloom.cfg here are the options:
[JVMOptions]
-client
-Dfile.encoding=UTF-8

[JVMUserOptions]
-Xms512m
-Xmx1024m

REGRESSION. Last worked in version 8u45

ADDITIONAL REGRESSION INFORMATION:
I remember this was working on Mac OS 10.9 with Java 8 Update 40 and Java 8 Update 45.
I had opened a bug in a version earlier than Java 8 Update 40 which was fixed.
https://bugs.openjdk.java.net/browse/JDK-8094725
https://bugs.openjdk.java.net/browse/JDK-8095647

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create a Mac .app application.
In the build.xml you need to have the following

<fx:deploy verbose="true" width="800" height="600" outdir="${distDir}" outfile="Bloom" nativeBundles="all"><!--all -->
<fx:info title="Bloom" />
<!-- Mark application as a Swing app mainClass="ca.antaki.www.bloom.app.Bloom" -->
<fx:application id="Bloom" toolkit="swing" name="Bloom" mainClass="xyz" />
<fx:platform javafx="8.0+" ><!--basedir="" -->
<fx:jvmuserarg name="-Xmx" value="1024m" />
<fx:jvmuserarg name="-Xms" value="512m" />
<fx:jvmarg value="-client" />
<fx:jvmarg value="-Dfile.encoding=UTF-8"/>

</fx:platform>
<fx:resources>
<fx:fileset dir="${distDir}" includes="*.jar" excludes="jfxrt.jar" />
<fx:fileset dir="lib" includes="*.jar" excludes="jfxrt.jar" />
</fx:resources>
<fx:callbacks>
<!-- force use of default splash handler -->
<fx:callback name="onGetSplash">
(new dtjava.Callbacks()).onGetSplash
</fx:callback>
</fx:callbacks>
</fx:deploy>

In the plist file under /Users/USERNAME/Library/Preferences\Bloom.plist, you need to have the following:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>JVMUserOptions</key>
<dict>
<key>-Xmx</key>
<string>2048m</string>
</dict>
</dict>



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The expected result is that the Java has the value 2048m as an Xmx.
ACTUAL -
The value 1024m that I provided in the ant build.xml file

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
It takes multiple files to be able to generate a Mac Java app.
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None. If I remove the Xmx from the Bloom.cfg inside the Bloom.app it uses the default algorithm.

The bug only occurs on Mac 10.10, I don't have other versions of Mac therefore I don't know if they occur or not.
On Windows the bug doesn't occur.