When working with decimals with 3 decimal places, I get the weirdest issues.
Type .101 in A1 and type .102 in A2, Select both and then drag down series to
row 1000. At some point(usually around the 564th line) the numbers change
over to show about 15 decimal spaces. This throws off lookups or formulas
that require the numbers to be exact.

Also, when you drag down the numbers, the problem will go away once it
reaches 1.000, or I've seen where it will effect numbers in bunches.

Any ideas or suggestions would be appreciated.