One hour 5 minutes is the MCT to T4 to T4S, and physically it takes nearly exactly 30 minutes in my experience. Within T4 MCT is 55 minutes, if IB ticketed. Doors open + bus + valet baggage -> building is 10 minutes; T4 to T4S is 12 minutes; T4S, passports and to say Gate S43/S45 is 8 minutes. There is a "connections under 30 minutes" desk at passports, in the middle of the bank of desks.

I doubt they will rebook at Málaga since it's a legit connection and not really how IB staff normally operate anyway. But they will do it quite happily in Barajas if it is one ticket and you failed the connection. But you should be fine, it's actually plenty of time so long as your service leaves Málaga on time or thereabouts.

You sound like you are familiar with the set-up given your reference to the bus transfer. But the key thing to watch, as you enter the building off the bus is to go straight on toward the security scan machines - it's a sliding door that doesn't look like a door. It is signed on top. Don't turn left towards the baggage carousel as most passengers will be doing, or you'll end up accidentally landside. Then up one level (lift has no particular advantage), over to the left a few metres following the signs, then lift (massive advantage) down to the basement for the transit. Escalator up to passports, then lift to the main departure floor via the duty free shop experience.

I had a very recent experience of a 1 hr 5 minute transfer which was all IB and therefore booked at T4. It got retimed to 55 minutes - no problem, still within MCT. Then they reallocated a A340 to the service so IB transferred it to T4S and therefore it was outwith MCT. I expected to be rebooked, as one would with BA, but it wasn't - in any case I made the connection no problem at all and probably had 10 or so spare minutes.