Today ArcMap has decided that when I use the "Select By..." tool from the Tools menu bar, everything will get selected regardless of whether the feature was inside of the selecting rectangle/circle and whether or not the feature/shapefile was selectable or not. Using the attribute table to select a single row does yield only the single feature that was selected, so this issue may not be necessarily systemic to whatever code controls selection.
System Information: Standalone workstation, Win 7, ArcGIS 10.0
Strange... You have multiple records, so we are not dealing with a single multipart feature. I don't think a relationship class could be causing this... Maybe something with the coordinate systems (data frame vs featureclass)...
In what format is the data? If is resides in a file geodatabase, do you see any negative areas? Could you run a Repair Geometry—Help | ArcGIS for Desktop (10.3 link, but tool is available too in 10.0)?
Are you willing to share the data to see if this can be reproduced? If not, could you share some screen shots of what is happening?
Unfortunately I am unable to share the data due to security and other pesky ruled regardless of the content of the actual data.
The issue occurs with any spatial data, features in a gdb, shapefiles, or KMLs, that is added to ArcMap.I tried restarting Arc and the system to see if that would correct the issue but that did not fix anything.
My main worry though is whether something is very wrong considering it will select data that I have made non-selectable.
Not sure if this is what is causing the specific issue you mention, but I will bring this up for others who have Selection issues and read this post. It may be that the Interactive Selection Options are set differently than expected. I've gotten tripped up by this at times when instead of the default "Create New Selection" the selection gets changed to a different method.
Chris Donohue, GISP
Unfortunately changing this setting does not fix anything. Regardless of the option activated, ArcMap still selects all spatial data whether it's been identified as selectable or not.
Another setting to check, on the off chance that it is causing the issue:
Selection, Selection Options:
Make sure the Tolerance value is not a large number, or it may cause selection far beyond the intended extent.
Chris Donohue, GISP
That was one thing I did check and my system is also set to a tolerance of 3. But even if this were the issue, why are non-selectable features being selected.