Steps to reproduce:

1. Create a custom field in JIRA
2. And insert in this custom field, for example this code:

   umcs_43243=153253240501
   umcs_saddsafsdafow=140532501
   umcs_owsdafas12=1dzs40fdsafs01
   

3. Now, go to your Confluence, in the Jira issue macro, and past the XML from JIRA.
4. And press refresh
5. You'll see that will return umcs_43243=153253240501 <br/> umcs_saddsafsdafow=140532501 <br/>

Workaround:

There's no workaround yet.