dspsr labels archives with wrong epochs. This has been observed when using dspsr -turns but I don't think it's related to this option. I vaguely remember this also happens in single pulse mode. I suspect this happens always but for the usual 10 second integrations of MSPs no one notices offsets of 1 or 2 pulse periods.
As I hinted in the last sentence, the epochs are typically off by an integer number of periods, possibly only by one period. Not all the files get labeld with a wrong epoch.
This bug probably matters only in single-pulse mode and I've updated the title to reflect this. (Was this bug ever fixed?)