It seems that there is a bug in CRM Dynamics within the Import Solution mechanism - Case sensitivity for publisher ID (UniqueName) matching is not consistent:
When importing a managed solution for the first time the publisher ID matching is case insensitive. Thus a solution with publisher id DefaultPublisheriTechcom2 is matched with existing publisher id DefaultPublisheriTechCom2 (letter C is uppercase case) (provided that there is such publisher in the target org that the solution is being imported to). Thus no new record is created (as part of the import process) on behalf of the imported solution publisher.
When importing the solution for the 2nd time with the same name as the 1st one (for purpose of updating the 1st imported solution, or as a new other solution exported from an org that is different from the 1st one, but has created a solution with same name) the import fails with an error such as the following:
The following managed solution cannot be imported: TestSolution. The publisher name cannot be changed from DefaultPublisheriTechCom2 to DefaultPublisheriTechcom2.
So, in the 2nd time the publisher ID matching is case sensitive, and thus the import fails.
A workaround for this bug is to edit the solution.xml file within the zipped exported solution and change the publiser id to match the publiser id of the solution within the target org the solution is being imported to. E.g. change within solution.xml the publisher ID (UniqueName) from DefaultPublisheriTechcom2 to DefaultPublisheriTechCom2 (letter C is upper case).