Photoshop Never Deallocates Memory

Ten step guide: How to test if Photoshop is able to deallocate unused memory:

01) Exit Photoshop if it's already running. Start it up again.
02) Open the task manager and go the the "Performance" tab. Check the total memory usage in gigabytes. (Green letters in Windows 7, or the first number under "Memory" in Windows 10.)
03) Press Ctrl-N to create a new document. Pick 10000 x 10000 pixels, RGB, 16-bit per color channel.
04) MENU: Filter -> Noise -> Add noise, 50%
05) MENU: Filter -> Blur -> Blur
06) Now look at the memory usage in the task manager again. Notice how it's gone up multiple gigabytes. This is to be expected because it's a rather large file.
07) MENU: Edit -> Purge -> All
08) Notice how the memory usage did not drop.
09) MENU: File -> Close (choose "no" to saving the file)
10) Notice how the memory usage still did not drop, despite the fact that no data can now be restored. At this point there's no valid reason to keep the huge (empty) memory area allocated, thus making it unusable for other applications.

This might be by design, but I sure hope it's a bug. - Because deliberately designing something this way would be quite embarassing.

Tip to graphics artists running low on memory: You don't have to reboot your entire machine when this happens. Restarting applications written by Adobe is enough.