Bug 365219

FIrst off, this may be a problem with the panel, not the task manager, but I'm not sure. Its about the relationship between the two, so it's hard for me to guess the cause.

After adding a launcher to the icons only task manager widget via the context menu in the application launcher, if the panel's minimum size is smaller than the current size, the panel shrinks, and moves the last item in the task manager off screen. It looks like it's trying to put it into a new row, based on the animation, but the task manager settings are set to only allow 1 row.

This only seems to happen when adding a launcher in the above way, not when adding one from the context menu of the task manager itself.

Clicking the launcher fixes the problem, but only while the application is open. Also, launching another application after adding the launcher temporarily fixes the issue.

Restarting the plasmashell process, logging out, or restarting don't fix the issue.
The only fix I found was to remove the launcher from the task manager, or to remove the task manager from the panel and re-add it, which effectively does the same thing.

My guess is that un-launched launchers in the task manager take up more space than they are supposed to, and push whatever is after them into the next row, even if there is only one row. 

Reproducible: Sometimes

Steps to Reproduce:
1. Add a blank panel on the top or bottom of the screen, with a very small minimum size in order to make panel shrink to it's contents. (I used the smallest possible)
2. Add icons-only-task-manager widget and application launcher widgets to panel.
3. Change settings of task manager to have a maximum row of 1
4. Click application launcher, right click an application and select "Add as Launcher" from the context menu

Actual Results:  
The last item in the task manager animates off the screen as if it were being moved to a new row, even though there is no row.

Expected Results:  
The panel should resize itself to fit all icons within, not move an icon off screen.