On a 4k laptop with Linux Mint 17.3, using HiDPI, some icons (in file tabs) and some filetabs, as well as icons in the setting menus and check boxes are not scaled properly. I think using the HiDPI setting, they should be 2x bigger in size. The text is scaled correctly.
Kernel: Linux 3.19.0-32-generic (x86_64) Compiled: #37~14.04.1-Ubuntu SMP Thu Oct 22 09:41:40 UTC 2015 Default C Compiler: GNU C Compiler version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.3) Distribution: Linux Mint 17.3 Rosa Hardware: MSI GS72 6QE-206NL (Stealth Pro 4K) Resolution: 3840x2160 pixels
Current Kate master doesn't have such issues anymore, at least not with Qt >= 5.6/5.7