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I have encountered a weird problem with one of my OS X apps. The app uses AXAPI to create event taps and to monitor keyboard and mouse events. Some users with OS 10.6-10.7 report that when the app is active, their mouse doesn't function correctly - they have to click twice or more, otherwise system doesn't see the click at all.

When these users switched off AXAPI, the problem disappeared.

The weird thing is that I have never encountered this problem on development computers, nor did the testers. Yet around 10% of reporting users have experienced it.

I use active event tap at HID level and I also handle mouse events, but I never return NULL from callback.

The problem is almost certanly in AXAPI, but I can't understand where exactly it is.

ivanmoskalev
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    Sounds like there may be unwanted interaction with _another_ app. Is it possible for you to ask these users about other apps they run which might also use event taps? – jscs Jan 11 '12 at 18:54
  • I have asked so, and users reported that there are at least no mouse/keyboard utilities installed... Is it possible to implement, say, a logger that will somehow analyze other installed event taps - like ET Testbench does? – ivanmoskalev Jan 12 '12 at 08:12

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Eventually I switched to filtering Mouse Events with a separate passive EventTap. The problem disappeared after the update of the app, but there was also a minor OS X update around that time, so I can't actually tell what fixed the bug.

Josh, thank you for your idea anyway.

ivanmoskalev
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