This is a known Android issue which has been widely reported (example).
I saw a suggestion to use Call Delay Patch from the Android Market, but some report that this helps while others report that it doesn't work.
I have the same issue on my HTC Incredible S (Android 2.3.3) and want to know if this issue has been addressed already or if there is a patch for it or a way to avoid it. Searching the web brings only complaints.