Created attachment 163971 [details]
sample file

I found this issue while creating a unnitest for bug 135144 < https://gerrit.libreoffice.org/c/core/+/100157 >

Steps to reproduce:
1. Open attached document
2. Save it as ODT
3. Check styles.xml file or use https://odfvalidator.org/

-> Styles.xml uses field:fieldmark-start and field:fieldmark-end tags and the ODF validator claims is not allowed.

Reproduced in

Version: 7.1.0.0.alpha0+
Build ID: 58937aa4a50ecd681382f03331340da4c843b01e
CPU threads: 4; OS: Linux 4.19; UI render: default; VCL: gtk3
Locale: en-US (en_US.UTF-8); UI: en-US
Calc: threaded

and

Version: 5.2.0.0.alpha1+
Build ID: 5b168b3fa568e48e795234dc5fa454bf24c9805e
CPU Threads: 4; OS Version: Linux 4.8; UI Render: default; 
Locale: ca-ES (ca_ES.UTF-8)

but not in

Version: 5.0.0.0.alpha1+
Build ID: 0db96caf0fcce09b87621c11b584a6d81cc7df86
Locale: ca-ES (ca_ES.UTF-8)