The Conflict arise once the bug is not accept them as Open from development side. Time constraint also makes the reason for the Conflict. -Late Build/Short Test Time. -Giving Build and ask to test at end time of work day.
Conflict almost always arises through bad communication. If by user for example you mean tester then perhaps we can better answer your question. But if you mean user as in end user of the product then I would be surprised they come into conflict with each other. One of the roles as I see it of a tester is to be pedantic for example if in the tech spec or user requirements it states "click button A to print report. " Then that is what must happen. There is a bug if a) the report is printed without clicking and b) if clicking doesn't print a report. Now how do we communicate this to the developer? If you say hey your program is bugged it doesn't work then you are likely to have a conflict. If you say Hi on page 3 paragraph 4 user requirement XXX it states we must click button to have report But in fact this is not the case then your are more likely to make headway!
We often have conflict with the developer regarding the bug exists or not.
Sometimes bug itself is the not considered and fixed cause of estimation and budget constraints of the project.
Sometimes communication between the developer and tester are not setup properly cause of that developer may not able to interpret the bug properly.
And sometimes the inputs given by the testers are not enough for the developers to interpret and find the solutions so they seek for more information from testers.
Sometimes the developers says like the bug should be mapped to few requirements and if it is not mapped then it is not valid bugs. etc.
There may be several reasons of conflict with the developer. The following are scenarios where conflict can be arised:
1. Developer is too busy so s/he does not understand the defect properly. 2. Insufficient/incomplete information given at the time of defect logging. 3. Developer is not reproducing the defect in the environment as mentioned in the defect. 4. Developer could not understand whatever the defect is stating.