Mask: False ?!?

It's possible this is WAD (Working As Designed), but if it is, it's mightily confusing...

In the File Formats dialog I turned off a number of File Formats I would not (or only rarely) need. After restarting Cirrus, for all these File Formats, the Mask column in the list box suddenly shows "False" - and so does the corresponding text box on the General tab. (Screenshot 1)

Huh?, I think...

So, I try turning one of them back on again ... and apart from the checkbox itself, there's no change: still "False" in the Mask column and still "False" in the text box on the General tab. Has Cirrus forgotten the original mask? (Screenshot 2)

Then I try to "refresh" by selecting another FF, and then re-selecting the one I just turned back on. Now, the text box shows the original mask again (phew!), but the list box still shows "False". (Screenshot 3)

Surely this could be a little more intuitive? Such as showing the (stored) mask at all times and only changing the state of the checkbox and graying out the item in the list box when a FF is turned off?

(Now, what was I doing... ? oh yes, preparing for another bug report - tomorrow, it's bedtime now!)