Edit API does not save custom fields with comma

[rashed2014]

We tried to convert the comma to '%2C' Hex before sending it to RT. However, RT returns an error as such:
Can't use an undefined value as an ARRAY reference at /opt/rt4/share/html/REST/1.0/dhandler line 189.

Stack:
[/opt/rt4/share/html/REST/1.0/dhandler:189]
[/opt/rt4/share/html/REST/1.0/autohandler:54]
[/opt/rt4/sbin/../lib/RT/Interface/Web.pm:696]
[/opt/rt4/sbin/../lib/RT/Interface/Web.pm:375]
[/opt/rt4/share/html/autohandler:53]

Other special characters seem to be working with edit.