SYMPTOM:
After executing a grid report in Strategy Web, users can drag and drop attributes to pivot them to other locations on the grid or remove them from the grid entirely. However, sometimes users may notice that while they intend to only drag and drop a single attribute, multiple attributes may get selected during the drag and drop action, like shown below:

In this screenshot, both Year and Month are selected by the mouse click and hold action even though the intention was only to select the Year attribute.
CAUSE:
This may be caused by users selecting near the intersection of multiple attributes. This is a known issue in Strategy Web.
ACTION:
Contact Strategy Technical Support for an update on this issue.
WORKAROUND:
Users can right-click a single attribute of interest and use the context menu items to perform pivots, moves, or remove the attribute from the grid.
Users can also make sure to select the attribute away from any intersection points with adjacent attributes to perform the drag and drop.