my ability scores don't seem to last, when I level up I add to my strength and agility but the stats disappear to a lower setting. why is this happening, and can I avoid it?

Replied in the other thread:

"Been a while since I played, but I think you need to accept the changes for them to actually become permanent. Look for a checkbox or something like that."

If you leave the stats screen and then return and find that you still have those points to spend, then I think this is what's happening.

HereForTheBeer is correct; there is a bug if you distribute stat points, but do not apply the changes, then save the game and reload. That will result in the stat points being lost.
You can use iZakaroN's SaveEditor to replace the stat points, though.

When you first open the stat window, there is an X close button near the bottom, possibly hidden behind the toolbar UI interface if you are playing on lower resolutions (in that case, left click and hold to drag the window up). After you distribute stat points, the button turns to a checkmark to confirm those choices.
screenshot of the stat window (showing initial, levelled, distributed and confirmed stats)


If you wait long enough for any food/potion/spell effects to wear off and remove all equipment with stat bonuses (or make sure to take them into account), then the sum of

strength + agility + intelligence + constitution + any unassigned stat points

should be equal to

40 + 5*(Character Level) + other bonuses you would not have reached yet at low levels