This bug is very easy to reproduce. Create a directory called dirx. Inside it another directory called diry. Inside it another directory called dirz. Inside it a file called "file.txt". Filenames are not important, this is just an example.
Open dirx in windirstat. In this example it's on my desktop, but the location doesn't matter. You will see this:
So inside dirx are 3 items (diry, dirz and file.txt). The item number does not include the directory itself, as expected. This matches with WinDirStat's documentation which says: "Items: Number of items in the subtree. Sum of Files and Subdirs." So this is correct, no bugs here.
Now right-click on dirz and click Delete (or press Del on your keyboard). The view is updated to this:
These numbers are wrong. The number of items in the root is now 2, while we expect to see 1. If you right-click on either dirx or diry, and select refresh (or select it and press F5), the numbers are fixed:
assarbad 
WinDirStat
This bug is very easy to reproduce. Create a directory called dirx. Inside it another directory called diry. Inside it another directory called dirz. Inside it a file called "file.txt". Filenames are not important, this is just an example.
Open dirx in windirstat. In this example it's on my desktop, but the location doesn't matter. You will see this:
Files Items ------------------------------------------- C:\Users\you\Desktop\dirx 1 3 +- diry 1 2 +- dirz 1 1 +- file.txtSo inside dirx are 3 items (diry, dirz and file.txt). The item number does not include the directory itself, as expected. This matches with WinDirStat's documentation which says: "Items: Number of items in the subtree. Sum of Files and Subdirs." So this is correct, no bugs here.
Now right-click on dirz and click Delete (or press Del on your keyboard). The view is updated to this:
These numbers are wrong. The number of items in the root is now 2, while we expect to see 1. If you right-click on either dirx or diry, and select refresh (or select it and press F5), the numbers are fixed:
So to summarize the bug: the item count is not updated correctly when you delete a directory.