Hi @Lawrence D'Oliveiro (ldo),

this is because the extrude operator automatically sets the second transform orientation (double tapping) to normal mode, which is a sensible thing to do for extrusions. You can verify this by looking at the status message on the left in the viewport header after double tapping an axis key.

It says something along the lines of:

D: NUMBER (NUMBER) along SPACE AXIS

The reason it works after pressing ESC and double tapping an axis is that you are now doing a standard translation, which operates under the following rules:

1. single tap axis constraint is always in global space
2. double tap axis constraint is almost always in the space chosen in the viewport dropdown
3. exception to the rule above is when the dropdown is set to global space - the second space in this case is set to local

Also see the first paragraph in under Transform Orientations in the manual.

So, not a bug. :)

Why would this apply to X and Y, but not Z?

Here is something else to try:

• select a red face, then EKEY SKEY SHIFT-XKEY SHIFT-XKEY. The status message says “locking normal X”, but only allows you to scale the extrusion along the Z-axis.
• select a green face, then EKEY SKEY SHIFT-YKEY SHIFT-YKEY. The status message says “locking normal Y”, but only allows you to scale the extrusion along the X-axis.
• select a blue face, then EKEY SKEY SHIFT-ZKEY SHIFT-ZKEY. The status message says “locking normal Z”, but this time scaling of the extrusion happens along both X- and Y-axes.

So this time the message is consistent, but the behaviour still is not.

In T48481#375259, @Lawrence D'Oliveiro (ldo) wrote:

Why would this apply to X and Y, but not Z?

Because the extrusion operator is already locked in Z (normal space) when you press the EKEY. Pressing Z again releases the Z constraint. Again, see the status message in the header.

In T48481#375260, @Lawrence D'Oliveiro (ldo) wrote:

• select a red face, then EKEY SKEY SHIFT-XKEY SHIFT-XKEY. The status message says “locking normal X”, but only allows you to scale the extrusion along the Z-axis.
• select a green face, then EKEY SKEY SHIFT-YKEY SHIFT-YKEY. The status message says “locking normal Y”, but only allows you to scale the extrusion along the X-axis.
• select a blue face, then EKEY SKEY SHIFT-ZKEY SHIFT-ZKEY. The status message says “locking normal Z”, but this time scaling of the extrusion happens along both X- and Y-axes.

Works exactly as it says for me.

EKEY SKEY SHIFT-XKEY SHIFT-XKEY for example says it is locking the scale of the X axis in normal space. So the scaling can only happen on the Y and Z axis in normal space. And because the Pivot Point lies exactly on the the center of the selected face, scaling the Z axis doesn't change anything. As a result you only see change of scale on the Y axis in normal space.
When you change the Pivot Point to 3D cursor before you press those keys, you see that the scaling now also affects the Z axis in normal space.

So why does the Z axis behave differently from the others?

EKEY SKEY SHIFT-ZKEY SHIFT-ZKEY says it is locking the scale to the Z axis in normal space. So why does it not scale along Z in normal space?

OK, I think I’m beginning to understand now. Regardless of your choice of transform orientation, EKEY always starts out in Normal transformation mode. If you want your choice of transform orientation, you must ESC and then transform the extruded vertices in the usual way.