Cracked it!!
I am using AVG 8.0.238 Free and so is my friend; it is turned on for both sent and received messages.
I discovered that if an HTML message sent from Pegasus and received in OE6 was long enough for the AVG certification to be off-screen then, in reply (not in message view), the cursor would flash and after make a few minor text changes would lock up. However, if the message was short enough for the display window in OE6 to include the AVG certification then there was no problem at all.
My next test was to disable AVG for email checking and this was fine in OE6.
On inspection of the two received messages I noticed that the one with AVG turned on had ALT Boundary statements added with the certification (I do not understand quite how these statements work yet but I presume they are related to HTML/Text boundaries). With the message that was causing the cursor to flash, as soon as I hit reply in OE6 I went straight to the end of the message and deleted the certification plus the horizontal line (presumably resulting from the ALT Boundary statement). The cursor remained rock solid.
So I thought, how can I keep the AVG checking but not have the certification? Not having explored all the AVG settings I was, until an hour ago aware of the some of the controls available in AVG, I found:
Tools | Advanced Settings | E-mail Scanner | E-mail scanning | Certify e-mail I unticked both, resent the message and again The cursor remained rock solid.
So where is the failing?
1. It isn't in the way outgoing OE6 messages are handled by AVG as I have sent the same message and received in OE6 with AVG on without a problem.
2. Is it the structure of outgoing Pegasus messages and the way in which they interface with AVG?
3. Is it the way in which AVG handles Pegasus messages either outgoing, incoming or both?
4. Is it the way OE6 handles ALT-Boundary statements in Pegasus messages in Relpy mode?
Whatever, I have found the work-around but it isn't the solution - Turn off AVG Certification!
I hope this isn't too long-winded but it might serve others who may decided to analyse the issue deeper.
Mike