Apart from CH4-HD all the SD ones moved seamlessly from Astra 2A to Astra 1N a while ago. CH4-HD was recently off air for a while not because it moved transponder but because it's transponder was changed from DVB-S2 to DVB-S (the subject of the e-mail). There was a similar problem about a month ago. The epg kept getting cut short on a Saturday.
Channel 4-HD last changed transponder 22nd November last year when it moved from Eutelsat28A to Astra 1N.
23rd March 2012 (no retune was needed) Note the boob - FREEVIEW
Freeview HD Channel 4 planned outage
Dear Humax user,
Channel 4 have scheduled a change to the transponder that carries C4 HD.
The change will occur overnight on 27th March into early hours of 28th March – (23.00 to 03.00), and we therefore expect that C4 HD will be unavailable for a maximum of 4 hours at this time.
Humax freesat products will rescan for channels if left in Standby mode so the changes will be detected, however in the unlikely event that your product doesn't find this change or is powered off overnight a “freesat Tune” will be all that is required to fix this issue.