To be fair to the MStar line, it's not necessarily a bug that these boxes sometimes rescan channels automatically. Some other tuners do this as well.
For example, say the station adds or removes a subchannel, and you tune to one of the station's existing channels. Some tuners (e.g., my LG TV) will automatically detect the station's change and add or remove the affected subchannel automatically. Others (e.g., a DVR+) won't change anything until you rescan the channel manually. It just depends on the tuner firmware's design.
But there are things that do deserve the label "bug" IMO, even if HomeWorX customer support disagrees:
- Any customization (e.g., deleted, skipped, or renamed subchannels) is lost when an automatic rescan is triggered
- A rescan is often triggered without any noticeable change to the TVCT (IOW, no subchannels were added or removed, and the existing subchannels have the same channel numbers, subchannel numbers, and names)
- Most seriously, (and the reason I wrote that post) any timers for any subchannels on that station are lost.
Evidently, the HomeWorX and iView perform an automatic rescan by running the same procedure as a manual scan on that frequency: first deleting all existing subchannels, then letting the scan re-add them all. That might be OK for a manual scan, but an automatically-triggered one needs to tread more lightly.
Fortunately the latest iView firmware (probably HW too) seems to have addressed issue #2
at least. I used to get unwanted rescans every few days but since upgrading, I've only seen a few.