I didn't find this reported already, so if it's known, please ignore!
Admittedly, I brought this upon myself, but working on a smallish laptop keyboard sometimes I fat finger things. After stumbling into this on a couple of separate occasions, I thought it might be worth reporting.
I've done this on two different PC's, one running Windows 7 Pro and one running Windows 10 preview, and can easily duplicate this issue. Both are running PDN 4.0.5 I open an image. I go to resize, and in a hurry, type some value in the dimensions, but in my haste in this keyboard, I press the "-" next to the "0" key and hit Enter or click "OK". (Entered 220- for the dimension), and things hang. I will note that "Canvas size" dialogue, if I type a negative after the number, it greys out the OK button and converts the value in the text box to a negative. If I hit 'enter' the dialogue box goes away but otherwise nothing happens. This may also be buggish although it's preferable to the resize bug. The resize behaves differently in that if I type a - following the size value (ie. 220- pixels), the OK is greyed out (like in Canvas resize), but if I hit enter, the dialogue says "Initializing" with a "Cancel" option. If I do nothing it continues to say Initializing, if I click "Cancel" it changes to "cancelling".
Eventually, I have to open task manager and kill the process entirely.
Screenshots are in the attached album: https://plus.google.com/photos/111978587192129716116/albums/6142149637277308449?authkey=COTpsY3y-9HbDQ