Inconsistant Bug

Please, can any one give an example for a inconsistant bug.

In simple terms, the Bug which is not happenning consistently is defined as Inconsistent Bug. Suppose while doing rigorous testing if a tester is detecting a Bug with some set of input data and some set of process but by using the same data and the same process when it is tested another time the bug is not regenerated it is called as Inconsistent Bug.

The inconsistent Bug may happen mostly due to the
i. Deployment problem or
ii. due to environment problem
iii. or due to the system fluctuation.

If the software is not deployed properly and a bug is generated now and the same is tested after some point of time the bug may not be regenerated.

The bug generated when tested in one environment may not be regenerated while tested in another environment. For example the defect would have locked in the tester environment but at the developer side the defect would not have existed.

If the system fluctuates and does not behaves consistently the bug may also be inconsistent.

Following is an example of an Inconsistent bug:

In a library management system a reader wants to borrow a book and he clicks a available book from the directory and locks but at the same time another two readers are also locking the same book. In this case the system should throw an error that the book is locked for both the readers other wise it is a bug. But the system is showing error message for one of the reader but not the other. Here the bug is not consistent, as the error should happen all the times when the same book is locked for the second time...

example of an Inconsistent bug:
In an net search application , the user wants to search for a particular name through a web page which is connected to multiple databases on the same server, at the same time if couple of more users perform the same action then one of them would be getting HTTP 500 error--thats is nothing but broken page
This is due to the system fluctuation . Only one user gets this sought of message .and cant be reproduced again such sought of bugs are called Inconsistent bug

you come across these sought of bug while performing Performance test using j-meter on web pages interacting with several databases.