Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: AMD Radeon R9 200 Series ATI Technologies Inc. 4.5.13544 Core Profile Context 25.20.15011.1004
Broken: version: 2.80 (sub 57), branch: blender2.7, commit date: 2019-04-17 19:26, hash: rBb46245470f79
Short description of error
If an open window or split is in texture paint mode and another is in shader editor mode, changing a value in the shader editor then performing an undo does not undo the change. It appears in the undo history as if it has been (eye icon moves), but the undo is not applied. Undoing until you get to the past texture paint toggle applies the undo.
If you make multiple changes, none is undone until you undo the texture paint toggle.
Even when other actions are inbetween the value changes and the texture paint toggle, the shader editor changes are not undone until you get past the texture paint toggle. I.e., go to texture paint, draw a stroke, change something in shader editor, now you need to undo three times (change, stroke, texture paint toggle) before the change is undone in the shader editor.
Exact steps for others to reproduce the error
Default startup. Go to the "Texture Paint" tab. Switch the left split to shader editor mode. Change any value, e.g. the "Metallic" on the default Principled BSDF node. Undo (no noticed difference using the menu item vs. ctrl-z). The value change is not undone. Doing undo again, undoing the "Texture paint toggle" action undoes the value change (and leaves texture paint mode).