XML Stream Filter: Subfiltered JSON loses curly braces markup on merge

Attached: an xmlstream configuration to apply PCDATA subfiltering using the JSON filter, along with a simple testcase. The JSON is embedded like this:

#!xml
<json>{ 'key' : 'value' }</json>

On dev (0.30-SNAPSHOT), if I roundtrip this using tikal:

#!bash

/Applications/okapi-apps_cocoa-macosx-x86_64_0.30-SNAPSHOT/tikal.sh -fc okf_xmlstream\`@json.fprm` -x test.xml
/Applications/okapi-apps_cocoa-macosx-x86_64_0.30-SNAPSHOT/tikal.sh -fc okf_xmlstream\`@json.fprm` -m test.xml.xlf

I find that the surrounding '{' and '}' have been lost in the merge:

#!xml
<json> 'key' : 'value' </json>