An easy way to get around the whole "why didn't the probe droid come after luke and start shooting (or after Han and Luke and the Snowspeeders)" is that the probot's mission is to detect and record - kind of like a Forward Air Controller. FACs are sent behind enemy lines to record enemy locations and give latitude and longitude info for military bombardment.

So who is to say that the probot picked up Luke, Taun-Taun and Wampa and ever since was hiding behind the hills watching and recording. Hell, one could say that it was the whole events from Wampa to snowspeeder rescue that led the probot to the rebel base to begin with; all it had to do was track the snowspeeders and follow them to where they went.

It is the same meteor landing, or at least the same exact FX shot. That's why to take care of the "jump back in time" issue, just overlay a macro-binocular readout to the second meteor landing, take out the impact and replace it with a column of smoke (as we've already seen the probot land and leave) and then Luke gets womped. Being that the probot's first mission is to remain undetected so as to scour an entire planet for the rebels AND not alert them to it's presence, it would make sense that the probot could have flown over the hill that we see and was watching the entire Wampa attack all along. All it would need to do is wait to see if anything pans out, thus once the Snowspeeders arrived, it could follow them to their base.

Also remember that while it may have picked up Han and Chewie (in fact, it could have been approaching them for investigation after picking them up on its sensors), it blew itself up when Han and Chewie not only acknowledged it's existence but shot back. It was discovered and thus self-destructed to prevent capture.