* The 16-bit commands ADD HL,ss, ADC HL,ss and SBC HL,ss exist but not the command SUB HL,ss.
* When an LDxR / CPxR / INxR / OTxR instruction is interrupted, the interrupt handler sees some flags in a different state. [https://github.com/hoglet67/Z80Decoder/wiki/Undocumented-Flags#interrupted-block-instructions Source]
* The values of F5 and F3 following an SCF or CCF instruction depend on whether the preceding instruction modified the flags or not. [https://github.com/hoglet67/Z80Decoder/wiki/Undocumented-Flags#scfccf Source]
* The BIT b,(HL) instruction exposes certain bits of the internal register WZ to the undocumented flags F5 and F3. [https://zx-pk.ru/attachment.php?attachmentid=2989 Source]
* NMOS Z80 suffers a problem whereby LD A,I and LD A,R record the state of IFF2 after it has been reset if an interrupt is delivered during that instruction. [https://sinclair.wiki.zxnet.co.uk/wiki/Z80#LD_A,I_and_LD_A,R_bug Source]
* Z80 is always NMOS on CPC and Plus machines. [https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/z80-cpu-nmos-or-cmos/ Source]