Bugs are simply something that users will need to accept as being part of virtually any piece of software, and this includes mobile operating systems. Android has had its share of bugs over the years in various forms on various version of the platform. A more recent one that is being noticed by some users as of Android 5.1 Lollipop is not one to get overly stressed out over, but it is worth mentioning as people are likely experiencing it and are aware to some extent that it exists. The good news is that it doesn't hinder the ability to use the phone in any way and it isn't breaking things, which is always a good news.
The bug in question also at this point only seems to be affecting mostly Nexus devices like the Nexus 4, Nexus 5, Nexus 6, and Nexus 9 since these are for the most part, the only devices which have been updated to Android 5.1 Lollipop at this time. Having said this, it's entirely possible that if the bug isn't addressed by Google and fixed before Android 5.1 reaches other device types from OEMs that it could pop up there too. As mentioned above the bug is pretty minor and only seems to be affecting the notifications in the dropdown notification shade. Users experiencing the bug have been reporting via the issue tracker that when they have more than seven notifications lined up which use the standard Android notification service, a line at the very end of the notification string shows a string of numbers listed as "@17041057."
As stated by some of the users in the thread this can happen no matter which app the notification comes from as it seems to be a bug with the standard Android notification service. For long notification lists, Google reportedly places this notification ID tag at the bottom. If users are experiencing this bug, since it doesn't appear to affect anything negatively other than your annoyance factor being raised, it's not an issue that users should worry about as it will most likely be patched at some point in time, and eventually it will be a bug that fades out of existence.