My Scale tool has suddenly lost the ability to scale proportionally. When I hold down shift and drag diagonally nothing happens. It doesn't matter whether it's relative to the centre point or a different reference point.
It's driving me nuts and wasting heaps of time! Anyone got any ideas?
Have you tried resetting your preferences?
Have you installed anything new in your system recently?
Some browser plugins, Banking software, TeamView etc are known to mess with the modifier keys.
Which version of Illustrator are you using?
Not sure if the following steps reflect what the OP is experiencing, but it may be.
In Illustrator CC 2017 (21.0.2) on Sierra 10.12.3 I can see some disturbance when you try to scale proportionally with the Scale tool while Smart Guides are turned on and the Transform tools option is enabled in the Smart Guides preferences.
Steps to reproduce:
The problem does not exist in other Illustrator versions I know (for example CS5, CS6, CS2 or Illustator 10).
Would be nice to get some feedback if other users can reproduce this issue as well. If so, it qualifies as a bug.
Happening to me as well on Yosemite.
I haven't examined if it goes away with the steps you mentioned.
Happening here in Windows 7, but only when attempting to scale UP (dragging outward). (If I drag inward, it runs smooth and true.)
Kurt explains why. The culprit is the Transform Tools setting in the Smart Guides preferences panel. This setting disturbs shift dragging with a mouse or Wacom tablet. It also disturbs, shift-dragging points with VectorScribe's PathScribe tool. I've confirmed that with Astute Graphics.
Everything works for me as expected in the most up-to-date version of AICC 2017 on the most current Sierra, with the latest Wacom driver so long as the Transform Tools setting is toggled off.
I'm having the same problem after the latest illustrator CC update. Holding down SHIFT+OPTION does not scale an object proportionally from the centre like it used to. Holding down shift alone dow snot scale an object proportionally either, infact it flashes a proportionally called object for a split second randomly sometimes during the process. Seems like a bug to me. The thing that really irritates me about update sis how can the usual basic functions of any program be disrupted - where's the quality control Adobe?
Try this one.
View>Show Bounding Box (Ctrl/Cmd+Shift+B).
This is still happening in Illustrator 25.1, FOUR YEARS LATER. Fortunately, unchecking the transform tools checkbox in the Smart Guides preferences is still a valid workaround.