Lossy key combinations using the ALT modifier key on Windows-based machines

There are several scenarios that will be used for comparison:

Scenario 1: down ALT, down x, up ALT, up x
Scenario 2: down ALT, down x, up x, up ALT
Scenario 3: down ALT, up ALT, down ALT, up ALT
Scenario 4: down ALT, up ALT, down ALT, down x, up ALT, up x
Scenario 5: down ALT, up ALT, down ALT, down x, up x, up ALT

x was picked as it is a relatively neutral key in most browsers

Directions for repro

After this page loads, assuming no other clicks or focus within the webpage area, press the keys in the combinations shown in the scenarios

The difference column in the table below should be zero for both rows. If it is not then there is a mismatch between keydown/keyup pairs. The last column indicates the result of the number of keyUp events minus the number of keyDown events. A positive number indicates more key ups and a negative number indicates more key downs, i.e, keyUps are being lost.

What is essential in this repro is that the ALT key is the first key processed upon loading this page. In some browsers, pushing F5 is also considered a key that precedes the alt key (despite the page having been reloaded). In order to do a reload where ALT is processed as the first key, one needs to click on the address bar and push enter (assuming the page address is already in there).

Testing results--two browsers

The following table shows which keys are lost on several browser platforms tested.

	Scenario 1	Scenario 2	Scenario 3	Scenario 4	Scenario 5
IE7	x: up ALT: up	x: ALT: up	x: ALT: 2nd down	x: up ALT: 2nd up, 2nd down	x: ALT: 2nd up, 2nd down
Firefox3RC1	x: ALT: up	x: ALT: up	x: ALT: 2nd down	x: ALT: 2nd up, 2nd down	x: ALT: 2nd up, 2nd down

Press c to clear the results