When I initially start Krita, the tagging popup (right mouse click) for the brush preset dialog is hidden below the dialog. For brushes on the left side of the dialog this popup is completely hidden; for brushes on the right the popup shows partially.

To reproduce: after initial start (or a window resize), from menu bar, select 'choose brush preset', right-click to modify the tag of a preset.

I marked this "minor" because there is a workaround: close the dialog, then bring it up a second time. That is, the bug only appears the first time after starting Krita and there is no problem with the tagging functionality when the popup finally appears on top of the dialog.

I've been building from source, system information is,

Krita
  Version: 4.1.0-pre-alpha (git 650ef3d)

OS Information
  Build ABI: x86_64-little_endian-lp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: linux
  Kernel Version: 4.9.0-6-amd64
  Pretty Productname: Debian GNU/Linux 9 (stretch)
  Product Type: debian
  Product Version: 9

OpenGL Info 
  Vendor:  NVIDIA Corporation 
  Renderer:  "GeForce GTX 1050 Ti/PCIe/SSE2" 
  Version:  "4.5.0 NVIDIA 375.82" 
  Shading language:  4.50 NVIDIA 
  Requested format:  QSurfaceFormat(version 3.0, options QFlags(0x4), depthBufferSize 24, redBufferSize -1, greenBufferSize -1, blueBufferSize -1, alphaBufferSize -1, stencilBufferSize 8, samples -1, swapBehavior 2, swapInterval 0, profile  2) 
  Current format:    QSurfaceFormat(version 4.5, options QFlags(0x4), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 0, stencilBufferSize 8, samples -1, swapBehavior 2, swapInterval 0, profile  2) 
     Version: 4.5
     Supports deprecated functions true 
     is OpenGL ES: false