Do the steps as follow:
1. Go into the XenForo Bug Reports
2. Click Thread Display Options
3. Select Thread Creation Time
4. Click Set Option
I tested on XenForo Community too with both IE and Safari.
The left-bottom button for language will be disappeared after select any drop down list and go.
E.x:
change sort threads by to Thread creation time and set option, the button gone.
You can try other drop down list, I did tried others and same issue reduplicated.