Although I do not use my K7 or K5 regularly at this time with legacy lenses, I think I can help you understand the issue, and also the ways to work around it.
First of all, pentax DSLRs do not have inconsistent metering,
I say this because once you do some simple tests, you will find that the metering, while perhaps not correct, is very consistent in its errors.
To aid in this discussion, I have attached a chart that is very well known in the forums, which I really should update to include legacy lenses as well, but just have not had the time.
This is for K mounts, but shows for most of the flagship models (K20 missing but assumed identical to K10D) the performance with 50 mm lenses.
This is common for all focal lengths and leads me to believe that the metering is dependant on the true aperture of the lens, and therefore when an A lens is used, the camera corrects for the open aperture behavior
This also leads to errors when using teleconverters, which is how this whole thing came about.
To compound this issue, when using legacy lenses, which do not short any pins, there is, a model to model difference in some offsets in exposure that can be present. some models require an exposure compensation of 1-2 stops, and this may also change between manual mode and Av mode when using M42 lenses/
My advise is to use a block wall, paved road or other similarly uniform color, uniformly lit surface and map the performance of your metering system. once it is known, you will not have issues. As a simple point, if you shoot at F5.6 you will meter with the most consistency, I suspect this is because the kit lenses are all F4-5.6 lenses