Originally Posted by Martin Liddle:
“Best guess would be that you have set pre or post padding which on the 9300 (and 9150/9200) turns off series link and accurate recording. Set both values back to "on time" to restore series link.”
Yes, I think you are correct

. I emailed Humax with the same question, but also posted here, not thinking I'd get a reply from Humax having read here that they rarely reply, but I received the following from Grant at Humax within a few minutes of sending my question. I'm very impressed with them (and with Digital Spy as well of course!)
The series option will disappear if you have set the box to record 1-5 minutes before or after in the MENU. You will need to revert this back to on time or auto to get this feature back. If it is already on this then follow the steps below
Beware following these instructions will wipe your Recording Schedule,
You will NOT lose your already Recorded Programmes
1. Switch OFF the Humax Product from Electricity
2. Disconnect the Aerial cable From the Humax Product
3. Power On the receiver (Reconnect Electricity)
4. Press MENU
5. Select Installation on the Humax Remote
6. Enter your password (Default = 0000)
7. Select Default Setting and Press OK
8. Select Yes from the Pop Up Option and Press OK
9. Enter your password (Default = 0000)
10. The Humax product will now go Blank and then Reboot,
11. When the Humax Logo Appears Switch the Humax Product OFF
12. Connect the Aerial Cable
13. Power ON the Humax Product and It will automatically replace your Channels.