See test test_bitOrderOVC1.
This issue was discovered in the Link16 DFDL schema, and reproduced here in an isolated context.
This test shows that a spurious Runtime SDE is detected due to a bitOrderChange. This has to do with the unparser having to back-up to fill in a suspension for an outputValueCalc element, and losing the bitOrder that should be maintained/captured for that usage.
At least that's my theory.
This test should work, but gets a Runtime SDE:
edu.illinois.ncsa.daffodil.tdml.TDMLException: Runtime Schema Definition Error: Data output stream DOS(id=5, Active, Direct Absolute from 0 to 27 (length 27)) with bitOrder 'leastSignificantBitFirst' not on a byte boundary, cannot be populated from DOS(id=6, Finished, Buffered Absolute from 27 to 40 (length 13), data=1F000000000000000000000000000000 no following) with bitOrder 'mostSignificantBitFirst'.
Schema context: NNN Location line 64 column 18 in file:/tmp/s1_9132734461290850031.dfdl.xsd
Data location was preceding byte 3