A quick solution for your problem is to increase the row height a little bit so an entire char of the used font will be visible. You can do that before you populate your grid with the DefaultRowHeight property.
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The nature of this problem is in the new cell text editor reimplemented from scratch in iGrid 4.0 and based totally on WinAPI. We did that as we needed full Unicode editing support in our grid. In any case, we will work on the problem, and if we found a workaround, we'll implement it in the future builds of the control.