I found out that the problem lies on the xml file where all the syntax highlighting rules are defined (in this case, bash).
The specific file that contains bash syntax highlighting rules is modes/shellscript.xml
The fix was to add DELEGATE="LITERAL" on the rule where ${} syntax for variables is defined.
\modes\shellscript.xml
The bug fix was done in jEdit version 5.0.0
The screenshots of the program are available at:
before fix: http://bit.ly/XaMSEN
after fix: http://bit.ly/T2kHtV
applied in rev 22740, thanks