Windows 10 pro, DisplayFusion 8.1.2. Currently running 'creators update' of Win10, but problem existed also with 'anniversary update' and possibly before that (don't remember for sure, definitely several months at least). I don't remember for sure if this problem existed before 8.1.2 version of DF.

I use titlebar buttons a lot, several times per day. Occasionally, perhaps 5-10% of the time, when I click on a titlebar button it will perform its assigned task, but strangely will also open a Windows 10 app. Most often it is the 'photos' app, but not always. For example, just before creating this post I clicked on the titlebar button 'Send Window to Back' on a browser window. The browser did move to back, but the Windows app 'Alarms & Clock' opened as the frontmost window. I did not have 'Alarms & Clock' open before clicking the 'Send Window to Back' button. In each case, the Windows app was not open before clicking the DisplayFusion titlebar button. I just tried again by clicking on the 'Send Window to Back' button on this browser window, and after a couple of clicks of the button the Netflix Windows 10 app opened (it was not open before clicking the button). Sometimes the problem does not appear for a dozen or more clicks, sometimes it will happen 2-3 times in a row.

I have only noticed this problem with the 'Send Window to Back' button. I also commonly use the "Move Window to Different Monitor" button and I haven't noticed the problem happening with that button. I can't say for sure that it never happens with the other buttons, but it appears to only be the 'Send Window to Back' button that creates the problem.

Another strange thing -- I have only noticed this problem happening on the monitor which Windows identifies as #1, which is set as the primary monitor. I don't have a taskbar on that monitor, only on monitor #3. This information might be irrelevant, I don't know. It might just be that I do more 'send to back' on monitor #1; I don't know. I just tried to repeat the problem on other monitors and was unable to, yet could easily get the problem to happen on monitor #1. The random nature of the problem makes it hard to say for sure that it does not happen on other monitors.

It doesn't seem to matter what the window was that I click the 'Send Window to Back' button on; this problem happens when I click that button on browsers, explorer windows, programming IDEs, etc. I use the button, not the key combination. In fact, in an attempt to troubleshoot this problem I cleared the pre-assigned key combination and it didn't have an impact on the problem.