We are experiencing the same problem using EX03. All appointments appear on
the Terminal Server with OL03 client and on the T-mobile Dash but some
appointments disappear using both OL03 and OL07 on the local computer. When
you open the all appointments view, the missing appointments have no end
date. The fix is as you describe.

The only common denominator we have found is the mobile synchronization.
Have not seen the problem using BES.