Double ADSL filtering impacting service?

[#1]

Can the Plusnet Technical team and forum members assist with this question.
We had a phone socket downstairs that was double ADSL filtered, i.e. two ADSL filters connected and then the phone attached.
Upstairs, on a different phone socket (with one filter) we have the ADSL line attached to the Router.
After a power cut in my home location the ADSL service is impacted, an Engineer is called and after coming back from the local Exchange comes to my home address and notices the filters in tandem downstairs, one is removed and he states this was root cause.
I found this hard to believe since the configuration had not changed and the problem only occurred after the power cut within my home location (town) and to test the premise we 'double filtered' again and there was no issue.
So..question. Would double filtering a phone on one socket impact the ADSL service on another socket, and also after recreating the situation with no issue that this was in fact root cause.

[#2]

I didn't think double filtering should cause any problems, and I thought it even gets suggested sometimes for dealing with problematic devices. On the other hand, double filtering shouldn't be necessary.
If you're using plug in filters rather than a centralised filtered faceplate, your wiring set-up is probably less than optimal anyway. Unfortunately some engineers seem to want to do as little as possible to fix the problem, and blame the end user whenever possible.

[#3]

..one other reason why its important to get feedback is that Plusnet have also levied a BT Engineer call out fee....which I am attempting to dispute too but so far today I have struggled to get a satisfactory response.

[#4]

The engineer was talking hogwash, provided the double-filtering was just for a phone.