MUC subject changing leads to an account disconnect

[COM8]

Bevor you create a new issue:

- [ x ] I searched for similar issues and did not find one
- [ x ] I'm using the latest version available in the [Windows Store](https://www.microsoft.com/store/apps/9NW16X9JB5WV)

I'm submitting a...:

• Bug report (I searched for similar issues and did not find one)

Current behavior:

MUC subject changing leads to an accout disconnect and does not change the subject at all.

Expected behavior:

Just change the MUC room subject.

Minimal reproduction of the problem with instructions:

Environment:

App Version(s): 
v.0.7.1 <!-- Which version of the App are you using (e.g. v.0.2.0) -->

Windows 10 Version Number: <!-- https://en.wikipedia.org/wiki/Windows_10_version_history -->
- [ ] 1809
- [ x ] 1803
- [ ] 1709
- [ ] 1703
- [ ] 1607
- [ ] 1511
- [ x ] 1507
- [ ] Insider Build (build number: )
- [ ] Misc:

Device form factor:
- [ x ] Desktop
- [ x ] Mobile
- [ ] Xbox
- [ ] Surface Hub

Where did you got the APP from?
- [ x ] [Windows Store](https://www.microsoft.com/store/apps/9NW16X9JB5WV)
- [ ] Self-build, using a provided release source
- [ ] Self-build, repo cloned at [dd.mm.yyy] <!-- When did you clone the repo! -->
- [ ] Misc, got it from... <!-- Please tell us your source! -->