To everyone with the Calendar issues and everyone who is trying to figure it out:
I have a HTC One M7 Google Play Edition (Android 5.1) and yesterday I did a full wipe and installed the latest version of GPE rom. I didn't know about the Calendar issue, I did the wipe for other reasons.
Calendar was not installed so I didn't had to remove it, I used the latest TBO app to download the latest Clear version. After flashing it (together with 7 other TBO apps), it did not appear on my phone.
All the other apps were working.
Next step: I simply installed Calendar from Play Store (because I actually have a high need for Calendar on a daily or even hourly basis, I use it for work as well). Unfortunately, this gave me Calendar but NO WIDGET ! I tried rebooting and reinstalling from the Store. No change. I uninstalled, tried TBO again, Black and Clear. No Calendar. Eventually I used ES File Explorer Classic to find all appearances of "Calendar". I only removed the actual APK I could find. The other stuff ES found seemed to be "helper" services, I didn't dare to remove those. I rebooted twice and tried TBO again: no Calendar.
How I solved it: I installed the version from October 4th, got it from the
Resources page on the TBO homepage. Works flawlessly:
Clear version from Oct 4:
http://teamblackedout.com/Transparent/ClearGoogleCalendar5.6-133922642-LP-MM.zip
Black version from Oct 4:
http://teamblackedout.com/BlackedOut/BlackGoogleCalendar5.6-133922642-LP-MM.zip
So there is definitely something different with the 28-Oct version causing it not to work on some systems, even after a full wipe. But for me the Oct-4 version will do. I don't really update that often anyway.