zooming within a viewport

[lucylou]

(sometimes) when i use my roll button on the mouse to zoom out when im in the annotations of the viewport, (particularly when im editing a "roof" for some strange reason) the screen suddenly zooms right out and the viewport scale goes really small!!!! and i cant zoom in to 'undo' it, as its as though the scale of the page has changed. does anyone else have this problem? its a strange one i know! im on VW 12.5 and PC. thanks.