Avoid stutter on PC when switching on/off HDMI-connected TV

"As a sort-of answer to this question, I've now replaced the HTPC with a new one and the problem has disappeared. I can only assume that some mainboard/chipset limitation was causing this as I had tried both Nvidia and AMD/ATI video cards and various drivers with the old MSI-based Core 2 Duo system without success.

Based on the fact that hundreds of people have viewed this thread I can only assume my experiences were not unique, but for anyone else in the same siutation it's a bit disappointing to have reached the above conclusion.

For record, I'm now using a low-power AMD Zacate-based system using an Asus E35M1-M Pro and SSD and it compares very well with the older E6400 C2D system despite using about a fifth of the power and and space."

The problem is that turning on the TV uses more processing power and things are running to keep up. when there is no place to show video, it isn't going to waste power outputting video. I'm pretty sure that software could possibly get rid of it, but it's not really worth the work as it's expected by users and, as you mentioned, not life threatening.