I have never experienced any issue with a stuck lens. As you may know the camera reads the cassette's box speed and there is no way of setting the film's speed to another speed except by altering the coding on the cassette. If it cannot read the coding then the default is 100 ISA so if it's a 400 speed film which the camera cannot read such as cases where its bulk roll film or Foma film(see below) then the worst case is that you overexpose by two stops - not a disaster. The main problem arises with bulk roll film where the cassettes will not have any coding. You can use factory cassettes which have had their film processed or buy stick-on codes for re-usable cassettes.
There is no way to attach threaded filters to the lens for B&W and because the lens focuses by moving out to the correct position, holding a filter over the lens is problematic. You could buy resin filters and cut them to the size of the lens and carefully stick them on with blu-tac but frankly this will be a bit of a "faff".
It is said that Foma films will give some cloud rendition when you have white clouds in blue skies without a yellow filter so this might be worth a try. However Foma cassettes are not coded so you are back to attaching code stickers
The camera has a built-in flash so great for people shots indoors if the light is poor or people shots outdoors if fill-in flash is needed such as when you take a portrait style shot against the light when the face is in shadow. The flash is auto unless you switch it off but once you close the lens cover each time, you have to switch the flash off again.
The lens quality is superb and close focus is possible.
pentaxuser