The leader should remain selected after saving or loading; there is no setting to change that behaviour that I know of.
Does it matter where Jahan is in the party lineup? Did you try rearranging character portraits?
If you split Jahan off from the party and select a different character before saving, is Jahan still leader after loading?
Did you try verifying local files (for the Steam version)?
Please email supportdos@larian.com, with a description of the problem and the report.zip file generated by the
D:OS support tool (for the PC version). The report will contain system and game information, any crash dumps, and your saved games. If the file size is too large, you can delete most of the saves from the zip, since this issue is consistent.