There is a problem in how psrchive reads in psrfits files, specifically how it reads TEMPO1 polyco’s. Random erroneous digits are added after the 10 specified digits in the fractional part of the REF_MJD, which leads to jumps during observations when it switches to a new polyco-block.
Diff:
Lucas Guillemot and Ismaël Cognard detected this problem and provided a patch that fixes the bug.