Here's another weird one for your reading pleasure.

I have a pageframe with 4 pages, presented in a wizard-like style. When launched, only the first page is enabled. Clicking on a command button will enable the other pages and activate page 2. If I click a "Next" command button that's on page 2, this will activate page 3 and set focus to a spinner control. If I then click on page 2's tab, page 2 will activate as expected.

However, if I'm on page 2 and I click on page 3's tab instead of clicking the Next button and then attempt to click on page 2's tab, page 2 will not activate until I click it a second time. I turned on event tracking and found something very peculiar. When testing this scenario, I noticed that the click that doesn't work (the first one) does not generate a Click or MouseDown event, but a MouseUp event does occur. Any ideas as to what would prevent the MouseDown event from firing?