Yes, this would be expected when going from BASIC to HIGH coordinate reference precision.
Note that you are not going from "single to double precision", since ArcSDE has never used single precision, and HIGH precision is only 54-bits, not 64, because that is the size of the mantissa in IEEE double-precision values.
Maybe this will help you explain:
When "SDBE" was acquired by Esri, it made use of 32-bit integer arrays to store coordinate data. The integers were calculated explicitly by developers, by subtracting an offset and multiplying the remainder by a scale factor, and then rounding to the nearest integer. This resulted in reduced storage and faster comparison, because coordinate values were discrete.
Starting with SDE 3.0, Esri encapsulated the integer representation inside an "SE_SHAPE" object with a SE_COORDREF object to store the coordinate reference offsets and scales. The problem was that there was only 31 bits available for coordinates, and those that wanted more were unhappy. So at 9.0, The ArcSDE API was updated to optionally support the use of 64-bit integers in coordinate arrays, under the name "64_BIT" precision. ArcGIS did not use this capability until 9.2, by which time it was called "HIGH" precision, and was made the default.
Previously users had to carefully allocate their bits, but the additional space allowed for many options. Too many options, in fact, so a standardized set of coordinate references were calculated, with 0.1-1.0 millimeter precision in every possible projection. You can still change this, but it's difficult to override the default.
Unfortunately, the standardization came at a cost: Most users don't need sub-millimeter precision, especially for data that isn't accurate to a meter, and the storage cost of the compressed integer array at higher precision is significant. I often find I can use much less storage and see much better performance by using the old one million scale factor for decimal degree data, even if I now use a {-400,-400} origin.
Having read the Understanding Coordinate Management whitepaper, I would suggest you focus on the important components of the data extent -- the minimumX, minimumY, and XY precision. The upper-left upper-right corner can mind its own business, so long as it isn't interfering with storing values.
- V
