Description of problem: It's a design issue, not a functionality one. It'd be better if all the bars in the system tray KMix were at the same level for all apps. Some apps have a long title, and the titles is shown in full, which in return eats the space available for its sound bar. An example is the master channel (which is normally titled "Built-in Audio Analog Stereo") and the "Event Sounds" channel. Both channels might be set at 60%, but the short titled one appears to be set higher. Because they're not all on the same visual level, there's no reference point to compare sound levels. Reproducible: Always
I opened this bug on the Red Hat Bugzilla (https://bugzilla.redhat.com/show_bug.cgi?id=1078838) in March last year, but today I got a message saying it's closed due to EOL Fedora 20 Since it's really a KDE issue, not RH, I'm doing what I should have done in the first place. It's still present in Plasma 5
The KMix layout code has been updated and now ensures that all of the sliders and other GUI elements have the same size, even with long labels. Please reopen if this is still a problem with current KMix.